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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, Δ G, Δ H, and Δ S) 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. [ABSTRACT FROM AUTHOR]

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 (O ), 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 O 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. [ABSTRACT FROM AUTHOR]

The kinetics of the aquation reaction of [Ni(ODA)(H2O)3] (where ODA = oxydiacetate) promoted by [Fe(H2O)6]3+ ions were investigated. Spectrophotometric studies were carried out at temperatures within the range 293.15-313.15 K. The concentration of [Ni(ODA)(H2O)3] was 8.67 × 10-4 mol L-1 and the concentration of the [Fe(H2O)6]3+ ions was kept within the range 0.75 × 10-4 -7.50 × 10-4 mol L-1. The observable reaction rate constants increased with the increase of [Fe3+] according to the rate law: kobs = k + k1K {[Fe(H2O)6]3+}. Based on the kinetic data, the activation parameters were determined for the spontaneous step of the reaction and for the step dependent on the concentration of Fe3+ ions. A mechanism for the aquation reaction has been proposed. In the first step (the reversible part of the aquation reaction) a dinuclear intermediate product is produced and in the next step the products of the reaction, ([Ni(H2O)6]2+ and [Fe(ODA)(H2O)3]+), are formed. Nevertheless, it has turned out that the spontaneous path of the aquation reaction is also possible concurrently (independent of the presence of Fe3+ ions). However, this process is too slow to be accurately measurable. [ABSTRACT FROM AUTHOR]

The kinetics of substitution reactions of the CuODA and CuTDA binary complexes (ODA = oxydiacetate, TDA = thiodiacetate) with 1,10-phenanthroline (phen) and 2,2'-bipyridine (bipy) were studied in aqueous and DMSO solutions. These reactions were monitored spectrometrically using the stopped-flow method in the UV range. The studies were carried out at three temperatures - 298.15, 303.15 and 308.15 K. The concentrations of the binary complexes were kept within the range of 0.2-0.5 mmol L, whereas the concentration of phen or bipy was constant = 0.05 mmol L. The values of the reaction rate constants were calculated based on the A → B reaction model. A linear relationship of the rate of the substitution reaction versus the concentration of the binary complex as well as temperature was observed. The impact of the type of the primary (ODA and TDA) and auxiliary ligands (phen and bipy) as well as the effect of solvent on the rate of substitution reaction have been discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new oxidovanadium(IV) complex was prepared by the reaction of vanadyl acetylacetonate [VO(acac)2], iminodiacetic acid (H2IDA) and 1,10-phenanthroline (phen) in aqueous solutions. The crystal structure of [VO(IDA)phen]·2H2O was determined by X-ray diffraction crystallographic analysis. The stability of the title compound in aqueous solution was investigated by using potentiometric titration methods. Moreover, the kinetics of substitution reactions of the VO- (IDA) binary complex with 1,10-phenanthroline were investigated in aqueous solutions. These reactions were monitored spectrophotometrically at 249 nm by using stopped-flow methods. Kinetic measurements were performed in the 293-308 K temperature range, at different concentrations (0.1- 0.5 mM) of the binary complex and at a constant concentration of phen (0.05 mmol/L). Moreover, the antioxidant properties of this complex against superoxide radicals were studied by nitrobluetetrazolium (NBT) and cyclic voltammetry (CV) and the antioxidant properties were also investigated against two organic radicals: the 1,1-diphenyl-2- picrylhydrazyl radical (DPPH·) and the 2,2'-azinobis(3-ethylbenzothiazoline- 6-sulfonic acid) radical (ABTS·+) by using spectrophotometric methods. The results of the antioxidant tests show that VO(IDA)phen scavenges superoxide free radicals as well as organic radicals (ABTS·+ and DPPH·). [ABSTRACT FROM AUTHOR]

The aim of this work was to find a relationship between physicochemical properties of the oxovanadium(IV) complexes, namely [VO(ODA)(HO)], [VO(ODA)(phen)]·1.5HO and [VO(ODA)(bipy)]·2HO (ODA = oxydiacetate) as well as [VO(HO)], 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)]·2HO only. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The aquation reaction of the oxydiacetate cobalt(II) complex, namely [Co(ODA)(H2O)2]•H2O (ODA = oxydiacetate), induced by the Fe(III) ions as the promoter has been studied spectrophotometrically (UV-Vis). Kinetic measurements were carried out in the 283.15 - 303.15 K temperature range and at a constant ionic strength of 1.0 M (NaNO3). The observed rate constants were computed by a program based on global analysis. Furthermore, the reaction activation parameters were determined using the Arrhenius and Eyring equations. The changes in the enthalpy, entropy as well as activation energy barriers were calculated in the range of 0.00125 M - 0.125 M of the Fe(III) ion concentration. Based on kinetic data a mechanism for the aquation of the [Co(ODA)(H2O)3] complex has been proposed. [ABSTRACT FROM AUTHOR]

A potentiometric titration method (PT) and a stopped-flow kinetic technique monitored by a UV−Vis spectroscopy have been used to characterize the stability of series of Co(II)- and Ni(II)-thiodiacetato complexes, M(TDA), in the presence of 1,10-phenanthroline (phen) or 2,2'-bipyridine (bipy) in aqueous solutions. The stability constants of the binary (1:1), ternary (1:1:1) as well as the resulting hydroxo complexes were evaluated and compared to the corresponding oxydiacetate complexes. Based on the species distribution as a function of pH the relative predominance of the species in the system over a pH range was discussed. Furthermore, the kinetic measurements of the substitution reactions of the aqua ligands to phen or bipy in the coordination sphere of the binary complexes M(TDA) were performed in the 288-303 K temperature range, at a constant concentration of phen or bipy and at seven different concentrations of the binary complexes (0.2-0.5 mM). The kinetic stability of the M(TDA) complexes was discussed in relation to the experimental conditions and the kind of the auxiliary ligands (phen/bipy). Moreover, the influence of the type of primary ligand (thiodiacetate/oxydiacetate) on the substitution rate of the auxiliary ligands was also compared. [ABSTRACT FROM AUTHOR]

Thermal decompositions of the trans-[Co(en)Cl]Cl and cis-[Co(en)Cl]Cl complex isomers have been studied using the TG-FTIR and TG-DSC-MS techniques. The measurements were carried out in argon atmosphere over the temperature range 293-873 K. The influence of the configurational geometry on the pathways of thermal transformations was discussed. Furthermore, kinetic studies on the reaction of the cis- trans isomerization of the [Co(en)Cl]Cl complex salt in methanolic solutions were performed using UV-Vis spectrophotometry at five temperatures in the 293-313 K temperature range. The observed rate constants were computed using the 'Glint' program based on the global analysis. It has been found that the cis- trans isomerization of [Co(en)Cl]Cl is a first order reaction. Furthermore, the cis/trans [Co(en)Cl]Cl isomerization proceeds according to the dissociative mechanism. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Potentiometric (PT) and conductometric (CT) titration methods have been used to determine the stoichiometry and formation constants in water for a series of ternary complexes of Co(II) and Ni(II) involving the oxydiacetate anion (ODA) and 1,10-phenanthroline (phen) or 2,2′-bipyridine (bipy) ligands, namely [Co(ODA)(phen)(HO)], [Co(ODA)(bpy)(HO)], [Ni(ODA)(phen)(HO)] and [Ni(ODA)(bpy)(HO)]. The ternary complex formation process was found to take place in a stepwise manner in which the oxydiacetate ligand acts as a primary ligand and the phen or bipy ligands act as auxiliary ones. The stability of the ternary complexes formed is discussed in the relation to the corresponding binary ones. Furthermore, the kinetics of the substitution reactions of the aqua ligands in the coordination sphere of the Ni-ODA and Co-ODA complexes to phen or bipy were studied by the stopped-flow method. The kinetic measurements were performed in the 288-303 K temperature range, at a constant concentration of phen or bipy and at seven different concentrations of the binary complexes (4-7 mM). The influence of experimental conditions and the kind of the auxiliary ligands (phen/bipy) on the substitution rate was discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This study has demonstrated the direct formation of CO2 during the decomposition of the cis-[Cr(C2O4)(PM)(CO3)]− complex anion after addition of perchloric acid to the aqueous solution of this ion. Thus, the studied coordination species can be successfully used as a source of CO2 under specific conditions. This conclusion has been drawn from results of the kinetic studies of acid hydrolysis of the cis-[Cr(C2O4)(PM)(CO3)]− anion. This reaction was investigated using the stopped-flow technique. The measurements were carried out at temperatures ranging from 5 to 25 °C and in [H+] concentrations 0.01, 0.05, 0.1, 0.3, 0.5, 0.8, 1.1, 1.4, 1.7, and 2.0 M. The decarboxylation mechanism for the studied coordination compound has been proposed. [ABSTRACT FROM AUTHOR]

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 NO2 in biological milieu. The use of novel compound cis-[Cr(C2O4)(AaraNH2)(OH2)2]+ increases NO2 estimation accuracy by slowing down the rate of NO2 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, NO2 generation and cellular glutathione level. The severity of the process correlated positively with NO2 levels in pancreatic acinar cell cytosol samples, and negatively with cellular glutathione levels. [ABSTRACT FROM AUTHOR]