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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 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 reactivity of superoxide free radicals (O2·–) generated electrochemically towards the oxydiacetate metal complexes, namely [VO(oda)(H2O)2], [Co(oda)(H2O)2]·H2O, and [Ni(oda)(H2O)3]·1.5H2O (oda = oxydiacetate) was examined by cyclic voltammetry. The measurements were carried out in DMSO solution using a platinum electrode. Based on the height of the anodic peak Ea that corresponds to electrochemical oxidation O2·– O2 + e, in the absence and in the presence of the compounds in the mixture, their O2·– scavenge ability was assessed. The influence of the type of the complex was briefly discussed. H2O2 was used to induce cellular injury in a mouse hippocampal cell line (HT22). The cytoprotection of chemical compounds was tested at the mitochondrial (MTT test) and plasma membrane level (LDH leakage). Dose-dependent effect (10 and 100 μM of the complex) of investigated compounds was observed.

It has been found that the kinetics of acid-catalyzed hydrolysis of the [Co(NH3)4CO3]+ cation follows the rate law –d ln [complex]/d t = k1K[H+]/(1+K[H+]) (5 °C < T < 25 °C; 0.0543M < [HClO4] < 2.7M and I = 1.0M (NaClO4). The reaction course consists of a rapid pre-equlibrium protonation followed by a rate determining ring opening process and the subsequent fast release of monodentate carbonato ligand. The changes of the absorbance for the acidic aqueous solution of the [Co(NH3)4CO3]+ complex ion proceeded at relevant wavelength in the UV-Vis region and time course of these changes were analysed according to a programme “Glint” for the consecutive first – order reaction with two experimental rate constants kfast and kslow. Finally, the aquation mechanism has been proposed and the effect of ligand coordination mode (bidentate carbonato anion) on complex reactivity has been discussed.

Kinetics of the reaction of [tetraamminediaquacobalt(III)] perchlorate ion with carbon dioxide in aqueous solution was studied at various temperatures (5–25 °C), variable concentration of CO2 (0.005M; 0.01M; 0.015M) and over the pH range 6.04–8.15 at a fixed ionic strength of solution (1 M NaClO4). Investigations were carried out using stopped-flow spectrophotometry in the range of 300 – 700 nm. The results enabled determination of the number of steps of the reaction studied. Based on the kinetic equations, rate constants were determined for each step. Finally, the mechanism of carbon dioxide uptake by [tetraamminediaquacobalt(III)] perchlorate ion was proposed and discussed.