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The kinetics of the aquation reaction of [Ni(ODA)(H2O)3] (where ODA = oxydiacetate) promoted by [Fe(H2O)6]3+ ions were investigated. Spectrophotometry 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.

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)

The crystal structure of 2,2′-bipyridyl(iminodiacetato)oxidovanadium(IV) dihydrate of [VO(IDA)bipy]·2H2O molecular formula was redetermined. The vanadium atom has an octahedral coordination. The IDA ligand adopts the facial conformation in VO(IDA)bipy. The stability of title compound in aqueous solutions was investigated by using the potentiometric titration method. Furthermore, the kinetics of substitution reactions of the [VO(IDA)H2O]H2O binary complex with 2,2′-bipyridine was investigated in aqueous solutions. These reactions were monitored spectrophotometrically using the stopped-flow method at 260 nm. The kinetic measurements were performed in the 293–308 K temperature range, at different concentrations in the 0.1–0.5 mM range of the binary complex and at the constant concentration of bipy (0.05 mmol/L). The antioxidant properties of [VO(IDA)bipy]·2H2O and [VO(IDA)H2O]H2O complexes have been studied. The antioxidant activity of these complexes against the superoxide radical as well as stable organic radicals, namely 1,1-diphenyl-2-picrylhydrazyl radical (DPPH ) and 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical was investigated. The evaluation of [VO(IDA)bipy]·2H2O as a potential antioxidant agent shows that the titled complex exhibit the antioxidant activity against the superoxide anion and organic radicals.

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−1, whereas the concentration of phen or bipy was constant = 0.05 mmol L−1. 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.

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·).

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.

The isothermal titration calorimetry (ITC) technique supported by potentiometric titration data was used to study the interaction of zinc ions with pH buffer substances, namely 2-(N-morpholino)ethanesulfonic acid (Mes), piperazine-N,N'-bis(2-ethanesulfonic acid) (Pipes), and dimethylarsenic acid (Caco). The displacement ITC titration method with nitrilotriacetic acid as a strong, competitive ligand was applied to determine conditional-independent thermodynamic parameters for the binding of Zn(II) to Mes, Pipes, and Caco. Furthermore, the relationship between the proposed coordination mode of the buffers and the binding enthalpy has been discussed.

The influence of the different side chain residues on the thermodynamic and kinetic parameters for complexation reactions of the Co

The crystal structure of new 1,10-phenathrolin-1-ium aqua-(nitrilotriacetato-N,O,O',O")-oxidovanadium(IV) semihydrate of molecular formula (phenH)[VO(NTA)(H2O)]∙1/2H2O was determined. This is the first example of structurally characterized compound that comprises a distinctly separated, monomeric [VO(NTA)(H2O)](-) coordination entity. The crystallographic measurements have subsequently been complemented by the IR spectroscopic characterization and thermal analysis. Furthermore, the electrochemical (cyclic voltammetry) as well as spectrophotometric (UV-vis) studies revealed that the compound is capable of scavenging the superoxide free radicals (O2(-)) as well as stable organic radicals i.e. 2,2'-azinobis(3-ethylbenzothiazoline-6 sulfonic acid) cation radical (ABTS(+)) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), but its reactivity towards radicals is lower than that of VOSO4. Finally, biological properties of the complex in the range of 1-100 μM were investigated in relation to its cytoprotective activity against the oxidative damage generated exogenously by using hydrogen peroxide in the hippocampal neuronal HT22 cell line (the MTT and LDH tests). It has been established that in contrast to VOSO4 the title compound protects the HT22 from the oxidative damage. The paper presents a new perspective for oxidovanadium(IV) complexes as candidates for novel, low-molecular mass cytoprotective agents.

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.

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.

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.

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.