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The interaction between Eu(III) ion and different pH buffers, popular in biology and biochemistry, viz. HEPES, PIPES, MES, MOPS, and TRIS, has been studied by solution nuclear magnetic resonance spectroscopy (NMR) and time-resolved laser-induced fluorescence spectroscopy (TRLFS) techniques. The Good’s buffers reveal non-negligible interaction with Eu(III) as determined from their complex stability constants, where the sites of interaction are the morpholine and piperazine nitrogen atoms, respectively. In contrast, TRIS buffer shows practically no affinity towards Eu(III). Therefore, when investigating lanthanides, TRIS buffer should be preferred over Good’s buffers.Graphical abstract

In this review, primary attention is given to the antioxidant (and prooxidant) activity of polyphenols arising from their interactions with iron both in vitro and in vivo. In addition, an overview of oxidative stress and the Fenton reaction is provided, as well as a discussion of the chemistry of iron binding by catecholate, gallate, and semiquinone ligands along with their stability constants, UV-vis spectra, stoichiometries in solution as a function of pH, rates of iron oxidation by O₂ upon polyphenol binding, and the published crystal structures for iron-polyphenol complexes. Radical scavenging mechanisms of polyphenols unrelated to iron binding, their interactions with copper, and the prooxidant activity of iron-polyphenol complexes are briefly discussed.

The cyclic voltammetry of pyridine-2,6-dicarbohydrazide (H 2 P) was performed in three different solutions with 0.1 M concentration of KCl, NaOH, and HCl. The pH value for the supporting electrolytes varies from acidic (4.30), alkaline (9.06), and neutral (6.96). Different cyclic voltammograms were obtained in the used media and discussed as follows: no cathodic or anodic peaks of ligand was observed in neutral medium whereas in acidic solution, only reduction peak detected at − 0.56 V but in case of basic solution, both reduction and oxidation peaks appeared at − 0.06 and 0.18 V, respectively. The addition CuCl 2 was also revealed to develop and explain the interaction of Cu 2+ with the ligand in the applied media. The redox process of copper ion and ligand species appeared in using 0.1 M NaOH as a quasi-reversible wave and diffusion-controlled reaction. Upon application of 0.1 M HCl a detectable redox reaction of Cu 2+ was observed in addition to the H 2 P ligand was only reduced through an irreversible process. The high evaluated stability constants and Gibbs free energies of complexation on Cu 2+ -H 2 P systems in both acidic and basic-enriched supporting electrolytes refer to the formation of stable coordinate complexes in solution measurements. Graphical abstract

The hydrolysis behavior of U(IV) was preliminarily explored by experimental methods, and the hydrolysis characteristics of U(IV) were determined. The results show that the absorption characteristic peak of U(IV) hydrolyzed products is between 380 and 420 nm, the hydrolytic process is not linear and reversible, and the hydrolysis reaction of U(IV) includes multiple processes. There are 4 integer hydrolysis stability constants of U(IV) were experimentally analyzed. With the increasing of OH − concentration, the mean coordination number of OH − increases.

Adequate micronutrient concentrations in crops are essential for human health and agricultural productivity. However, 30% of plants growing on cultivated soils worldwide are deficient in iron (Fe). Because of low micronutrient bioavailability, graminaceous plants have evolved to exude small molecules, called phytosiderophores, into the soil environment, which strongly complex and promote uptake of trace elements. The development of a synthetic phytosiderophore, proline-2′-deoxymugeneic acid (PDMA), has been shown to promote Fe uptake in rice plants; however, its binding capabilities with other metals, which may impact the ability to promote the uptake of Fe and other trace nutrient metals commonly found in soils, remain unknown. We conducted spectrophotometric titrations to determine the stability constants (logK) of PDMA complexes with Mn(II), Co(II), Cu(II), Ni(II), and Zn(II). We determined that PDMA complex stability constants correlated with: (1) the hydrolysis constants of metal ions (logKOH) in complexes; (2) the ionic potential of complexed metals; and (3) the corresponding complex stability constants of other mugineic acid type phytosiderophores, as well as the trishydroxamate microbial siderophore DFOB. These correlations demonstrate the potential, and limitations, on our ability to predict the stability of phytosiderophore complexes with metal ions with different physicochemical properties and with potentially different coordination structures.

2-Hydroxy-3-nitro-5-ethylphenylphosphonic acid (H 3 L 4 ) and its diethyl (HL 5 ) and monoethyl (H 2 L 6 ) esters were synthesized as part of our continuing research on physicochemical and biological properties of coordination compounds of bioactive metal ions with 2-hydroxyphenylphosphonic acid derivatives. The protonation constants of the compounds H 3 L 4 and H 2 L 6 and the stability constants of copper( ii ) complexes with the acid H 3 L 4 were determined by potentiometric titration in water. The complex [Cu(H 2 L 4 ) 2 (H 2 O) 2 ] was synthesized and its structure was suggested based on the elemental analysis data, IR spectra, electronic absorption spectra, and DFT calculations. The toxicity of the acid H 3 L 4 and the complex [Cu(H 2 L 4 ) 2 (H 2 O) 2 ] was evaluated against the HeLa cancer cells (human cervical adenocarcinoma) and the protective effect of these compounds was studied under oxidative stress induced by hydrogen peroxide in HeLa cells.

In this work, interactions of mercury with di allyl disulfide (DADS), dimethyl disulfide (DMDS), and diallyl sulfide (DAS) were studied by differential pulse voltammetry. A thorough investigation was carried out on the complexation of mercury(II) by the garlic organosulfur ligands DADS, DMDS, and DAS at different steps. The optimal measurement conditions were conducted to determine the corresponding stability constants. The determination of stability constants of the labile mercury(II) with DADS, DMDS, and DAS complexes were based on the DE Ford-Hume methodology (equation) that calculated from the dependence of the shift of mercury(II) peak potential upon addition of the DADS, DMDA and DAS ligands separately. The results of this study provide evidence of the formation of 1:1 complexes between mercury(II) and DADS, DMDS, and DAS with the computed logβ1 values of the formation constants: (DADS): log β1 = 5.32 ± 0.46, (DMDS): log β1 = 5.40 ± 0.38, (DAS): log β1 = 4.61 ± 0.5 respectively.Graphic abstract

A novel model is presented for reliable estimation of the stability constants of the thiosemicarbazone ligands with different types of toxic heavy metal ions (log β 11 ) in an aqueous solution, which has wide usage in environmental safety and ecotoxicology applications. The biggest reported data of log β 11 for 120 metalthiosemicarbazone complexes are used for deriving and testing the novel model. In contrast to available methods where they need the two-dimensional (2D) and three-dimensional (3D) complex molecular descriptors as well as expert users and computer codes, the novel correlation uses four additive and two non-additive structural parameters of thiosemicarbazone ligands. The calculated results of the novel correlation are compared with the outputs of the genetic algorithm with multivariate linear regression method (GA-MLR) as one of the best existing methods, which requires seven complex descriptors. The estimated results for 78 of training as well as 42 of two different test sets were established by external and internal validations. The values of statistical parameters comprising average deviation, average absolute deviation, average absolute relative deviation, absolute maximum deviation, and the coefficient of determination for 73 data of training set of New model/GA-MLR are 0.04/ − 0.25, 1.06/1.31, 14.4/18.7, 3.18/7.92, and 0.830/0.652, respectively. Thus, the predicted results of the new model are worthy as compared to the complex GA-MLR model. Moreover, assessments of various statistical parameters confirm that the new model provides great reliability, goodness-of-fit, accuracy, and precision.

Thermodynamic equilibria and concentrations in thermodynamic equilibria are of major importance in chemistry, chemical engineering, physical chemistry, medicine etc. due to a vast spectrum of applications. E.g., concentrations in thermodynamic equilibria play a central role for the estimation of drug delivery, the estimation of produced mass of products of chemical reactions, the estimation of deposited metal during electro plating and many more. Species concentrations in thermodynamic equilibrium are determined by the system of reactions and to the reactions’ associated stability constants. In many applications the stability constants and the system of reactions need to be determined. The usual way to determine the stability constants is to evaluate titration curves. In this context, many numerical methods exist. One major task in this context is that the corresponding inverse problems tend to be unstable, i.e., the output is strongly affected by measurement errors, and can output negative stability constants or negative species concentrations. In this work an alternative model for the species distributions in thermodynamic equilibrium, based on the models used for HySS or Hyperquad, and titration curves is presented, which includes the positivity of species concentrations and stability constants intrinsically. Additionally, in this paper a stabilized numerical methodology is presented to treat the corresponding model guaranteeing the convergence of the algorithm. The numerical scheme is validated with clinical numerical examples and the model is validated with a Citric acid–Nickel electrolyte. This paper finds a stable, convergent and efficient methodology to compute stability constants from potentiometric titration curves.

Here, we describe two sets of thermodynamic ionic radii (r1 and r2) of lanthanide ions derived from the analysis of large set of the stability constants logβ1 and logβ2 of the ML and ML2 complexes of lanthanide ions M (from Ce3+ to Lu3+) with organic ligands (L) in water. It has been demonstrated that the stability constants of two metals Mi and Mj with a given ligand L are related by simple equations logβ1j = r1i/r1j.logβ1i and logβ2j = r2i/r2j.logβ2i which formally correspond to purely electrostatic interactions between spherical cations with organic molecule. Predictive performance of these equations was assessed in fivefold cross-validation procedure. The standard deviation (s) of predictions varies from 0.3 to 1.0 for logβ1 and from 0.4 to 1.2 for logβ2 as a function of the difference of Shannon ionic radii (Δrij) of Mi and Mj: s1 = 0.27 + 4.25Δrij for logβ1 and s2 = 0.39 + 5.16Δrij for logβ2. The new radii r1 and r2 steadily decrease across the Ln series, i.e., they follow the same trend as Shannon effective radii of lanthanide ions. The calculations were performed using experimental data on 2854 logβ1 values for 445 organic ligands and 947 logβ2 values for 156 organic ligands in the complexes with 13 metals.