Simultaneous determination of thermodynamic and kinetic parameters of aminopolycarbonate complexes of cobalt(II) and nickel(II) based on isothermal titration calorimetry data.

The influence of the different side chain residues on the thermodynamic and kinetic parameters for complexation reactions of the Co2+ and Ni2+ ions has been investigated by using the isothermal titration calorimetry (ITC) technique supported by potentiometric titration data. The study was concerned with the 2 common tripodal aminocarboxylate ligands, namely, nitrilotriacetic acid and N-(2-hydroxyethyl) iminodiacetic acid. Calorimetric measurements (ITC) were run in the 2-(N-morpholino)ethanesulfonic acid hydrate (2-(N-morpholino) ethanesulfonic acid), piperazine-N,N'-bis(2-ethanesulfonic acid), and dimethylarsenic acid buffers (0.1 mol L-1 , pH 6) at 298.15 K. The quantification of the metal-buffer interactions and their incorporation into the ITC data analysis enabled to obtain the pH-independent and buffer-independent thermodynamic parameters (K, ΔG, ΔH, and ΔS) for the reactions under study. Furthermore, the kinITC method was applied to obtain kinetic information on complexation reactions from the ITC data. Correlations, based on kinetic and thermodynamic data, between the kinetics of formation of Co2+ and Ni2+ complexes and their thermodynamic stabilities are discussed.

Physicochemical properties of ternary oxovanadium(IV) complexes with oxydiacetate and 1,10-phenanthroline or 2,2'-bipyridine. Cytoprotective activity in hippocampal neuronal HT22 cells.

The aim of this work was to find a relationship between physicochemical properties of the oxovanadium(IV) complexes, namely [VO(ODA)(H2O)2], [VO(ODA)(phen)]·1.5H2O and [VO(ODA)(bipy)]·2H2O (ODA = oxydiacetate) as well as [VO(H2O)5](2+), and their biological activity. A potentiometric titration method has been used to characterize the stability of the complexes in aqueous solutions. Furthermore, the reactivity of the complexes towards superoxide free radicals was assessed by employing the NBT assay as well as a cyclic voltammetry (CV) technique. Additionally, the investigations of the antioxidant properties of the complexes were complemented by studying their reactivity towards organic radicals (the ABTS and DPPH tests). Finally, the biological properties of the complexes were investigated in relation to their cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the Hippocampal neuronal cell line HT22 (the MTT and LDH tests). The obtained results showed that all the compounds under study display antioxidant properties but a concentration-depended protective effect against the oxidative damage was found for [VO(ODA)(bipy)]·2H2O only.

Cis-[Cr(C2O4)(pm)(OH2)2]+ coordination ion as a specific sensing ion for H2O2 detection in HT22 cells.

The purpose of this study was to examine the application of the coordinated cis-[Cr(C2O4)(pm)(OH)2]+ cation where pm denotes pyridoxamine, as a specific sensing ion for the detection of hydrogen peroxide (H2O2). The proposed method for H2O2 detection includes two key steps. The first step is based on the nonenzymatic decarboxylation of pyruvate upon reaction with H2O2, while the second step is based on the interaction of cis-[Cr(C2O4)(pm)(OH2)2]+ with the CO2 released in the previous step. Using this method H2O2 generated during glutamate-induced oxidative stress was detected in HT22 hippocampal cells. The coordination ion cis-[Cr(C2O4)(pm)(OH2)2]+ and the spectrophotometric stopped-flow technique were applied to determine the CO2 concentration in cell lysates, supernatants and cell-free culture medium. Prior to CO2 assessment pyruvate was added to all samples studied. Pyruvate reacts with H2O2 with 1:1 stoichiometry, and consequently the amount of CO2 released in this reaction is equivalent to the amount of H2O2.

A novel biosensor for evaluation of apoptotic or necrotic effects of nitrogen dioxide during acute pancreatitis in rat.

The direct and accurate estimation of nitric dioxide levels is an extremely laborious and technically demanding procedure in the molecular diagnostics of inflammatory processes. The aim of this work is to demonstrate that a stop-flow technique utilizing a specific spectroscopic biosensor can be used for detection of nanomolar quantities of NO(2) in biological milieu. The use of novel compound cis-[Cr(C(2)O(4))(AaraNH(2))(OH(2))(2)](+) increases NO(2) estimation accuracy by slowing down the rate of NO(2) uptake. In this study, an animal model of pancreatitis, where nitrosative stress is induced by either 3g/kg bw or 1.5 g/kg bw dose of L-arginine, was used. Biochemical parameters and morphological characteristics of acute pancreatitis were monitored, specifically assessing pancreatic acinar cell death mode, NO(2) generation and cellular glutathione level. The severity of the process correlated positively with NO(2) levels in pancreatic acinar cell cytosol samples, and negatively with cellular glutathione levels.

Influence of Primary Ligands (ODA, TDA) on Physicochemical and Biological Properties of Oxidovanadium (IV) Complexes with Bipy and Phen as Auxiliary Ligands.

The influence of the oxydiacetate (ODA) and thiodiacetate (TDA) ligands on the physicochemical and biological properties of the oxidovanadium(IV) ternary complexes of the VO(L)(B) type, where L denotes ODA or TDA and B denotes 2,2'-bipyridine (bipy) or 1,10-phenanthroline (phen), has been investigated. The stability of the complexes in aqueous solutions, assessed based on the potentiometric titration method, increases in the following direction: VO(TDA)(bipy) < VO(ODA)(bipy) < VO(TDA)(phen) < VO(ODA)(phen). Furthermore, the influence of the TDA and ODA ligands on the antioxidant activity of the oxidovanadium(IV) complexes toward superoxide free radical (O2•-), 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS+•) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH•) has been examined and discussed. The reactivity of the complexes toward O2•- increases in the following direction: VO(TDA)(phen) < VO(TDA)(bipy) ≈ VO(ODA)(bipy) < VO(ODA)(phen). The antioxidant activity against ABTS+• and DPPH• free radicals is higher for phen complexes, whereas the thiodiacetate complexes are more reactive than are the corresponding oxydiacetate ones. Finally, herein, the cytoprotective activity of the complexes against the oxidative damage generated exogenously by hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests) is reported. In a low concentration (1 µM), the cytoprotective action of thiodiacetate complexes is much higher than that of the corresponding oxydiacetate complexes. However, in the higher concentration range (10 and 100 µM), the antioxidant activity of the complexes is overcompensated by their cytotoxic effect.

Physicochemical and biological properties of oxovanadium(IV), cobalt(II) and nickel(II) complexes with oxydiacetate anions.

The potentiometric and conductometric titration methods have been used to characterize the stability of series of VO(IV)-, Co(II)- and Ni(II)-oxydiacetato complexes in DMSO-water solutions containing 0-50 % (v/v) DMSO. The influence of DMSO as a co-solvent on the stability of the complexes as well as the oxydiacetic acid was evaluated. Furthermore, the reactivity of the complexes towards superoxide free radicals was assessed by employing the nitro blue tetrazolium (NBT) assay. The biological properties of the complexes were investigated in relation to their cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the Human Dermal Fibroblasts adult (HDFa) cell line as well as to their antimicrobial activity against the bacteria (Bacillus subtilis, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis). The relationship between physicochemical and biological properties of the complexes was discussed.

Fluorescence quenching of fluoroquinolone antibiotics by 4-hydroxy-TEMPO in aqueous solution.

The fluorescence quenching of norfloxacin, danofloxacin, enrofloxacin and levofloxacin, belonging to a group of fluoroquinolone antibiotics, by 4-hydroxy-TEMPO was studied in aqueous solutions with the use of steady-state, time-resolved fluorescence spectroscopy as well as UV-VIS absorption spectroscopy methods. In order to understand the mechanism of quenching the absorption and fluorescence emission spectra of all fluoroquinolone antibiotics studied as well as decreases of their fluorescence were registered as a function of the 4-hydroxy-TEMPO concentration. No deviations from a linearity in the Stern-Volmer plots (determined from both, steady-state and time-resolved measurements) were observed. The fluorescence quenching mechanism was proved to be totally dynamic, what was additionally confirmed by the registration of Stern-Volmer plots at 5 temperatures ranging from 15 to 55°C. On the basis of theoretical calculations of fluoroquinolones' molecular radii and ionization potentials the mechanism of electron transfer was rejected. It seems that the fluorescence quenching is diffusion-limited and is caused by the increase of nonradiative processes, such as internal conversion or intersystem crossing. The Stern-Volmer quenching constants and bimolecular quenching constants were determined at the room temperature for all fluoroquinolone antibiotics studied.