Metal Coordination Properties of a Chromophoric Desferrioxamine (DFO) Derivative: Insight on the Coordination Stoichiometry and Thermodynamic Stability of Zr4+ Complexes

Desferrioxamine (DFO) is the current “gold standard” chelator for 89Zr4+, which is used to label monoclonal antibodies for applications in immunopositron emission tomography. Recently, controversial data have been reported regarding the speciation and the stability of the complexes formed by DFO with Zr4+ in solution. To shed some light on this point, we studied the coordination properties in solution ofa chromophoric DFO derivative bearing a substituted pyrimidine residue (DFO–Pm) toward several metal ions (Zr4+, Cu2+, Zn2+, Mg2+, Ca2+, Na+, K+). Potentiometric titrations showed that DFO–Pm and pristine DFO form complexes with very similar stoichiometry and stability. DFO–Pm, which can consequently be taken as a model system for DFO, provides a photochemical response to metal coordination that can be used to further define the complexes formed. In the critical case of Zr4+, spectrophotometric measurements allowed the verification of the formation of 1:1 and 2:3 complexes that, together with 2:2 complexes form the coordination model that was obtained through the use of our potentiometric measurements. Additionally, mass spectrometry measurements verified the formation of 1:1 and 2:3 complexes and showed that 1:2 species can be easily generated through the fragmentation of the 2:3 species. In conclusion, the results obtained with DFO–Pm validate the complexation model of Zr4+/DFO composed of 1:1, 2:2, and 2:3 metal-to-ligand complexes. Convergences and conflicts with other works are addressed.

Toward Unified pH of Saline Solutions

Fluctuations of pH in coastal systems are generally surveyed through potentiometric pH measurements. A new concept of a unified pH scale was introduced with the great advantage of enabling comparability of absolute values, pHabs, pertaining to any medium. Using water as an anchor solvent, yielding pHabsH2O, enables referencing the pHabs values to the conventional aqueous pH scale. The current work aims at contributing to implement pHabsH2O to saline solutions. To this purpose, differential potentiometric measurements, with a salt bridge of ionic liquid [N2225][NTf2], were carried out aiming at overcoming problems related to residual liquid junction potentials that affect the quality of such measurements. The ability to measure pHabsH2O with acceptable uncertainty was evaluated using Tris-Tris·HCl standard buffer solutions prepared in a background matrix close to the characteristics of estuarine systems (salinity of 20) as well as with NaCl solutions with ionic strength between 0.005 and 0.8 mol kg−1. The present study shows that for high ionic strength solutions, such as seawater, challenges remain when addressing the assessment and quantification of ocean acidification in relation to climate change. Improvements are envisaged from the eventual selection of a more adequate ionic liquid.

Study on regulators of purifying magnesite ore by cationic reverse flotation

The floatability of magnesite, dolomite and quartz is a major factor affecting the removal of silicon and calcium from magnesite ore. The effect of the regulators sodium hexametaphosphate (SH), sodium silicate (SS), trisodium phosphate (TP), tannic acid (TN) and monoammonium oxalate (OA) on the floatability of magnesite, dolomite, and quartz under the ether amine (EAH) system was studied. The results show that the five regulators have relatively little influence on the floatability of quartz and magnesite. Dolomite can be activated when the dosage of SH is less than 40 mg/L; however, dolomite can be inhibited when the SH dosage is greater than 40 mg/L. The other four regulators have inhibitory effects on dolomite, and TN and TP have strong inhibitory effects on dolomite. Under the conditions of optimum grinding fineness, pH and collector dosage, a recovery of approximately 70% and a concentrate with a grade of over 47% were obtained by three stages of reverse flotation using sodium hexametaphosphate and water glass as regulators and Haicheng magnesite ore with an SiO2 content of 2.38% and a CaO content of 0.75%. Potentiometric measurements and infrared spectroscopy analysis show that physical adsorption occurs between the three minerals and collectors, while the interaction of magnesite and dolomite with SH and SS involves both physical adsorption and chemical adsorption.

Design, Characterization, X-ray Single-crystal, Potentiometric Measurements, Molecular Modeling and Biomedical Applications of Thiosemicarbazones

Series of thiosemicarbazone compounds ((E)-2-((E)-1-(2-(p-tolyl)hydrazono)propan-2-ylidene)hydrazine-1-carbothioamide (TSC1), (E)-N-ethyl-2-((E)-1-(2-(p-tolyl)hydrazono)propan-2-ylidene)hydrazine-1-carbothioamide (TSC2) and (E)-N-phenyl-2-((E)-1-(2-(p-tolyl)hydrazono)propan-2-ylidene)hydrazine-1-carbothioamide)(TSC3) were synthesized and fully characterized by assistance of diverse physicochemical and spectroscopic tools like X-ray single-crystal, IR, mass, 1HNMR, Uv-Vis,…etc. potentiometric measurements, molecular modeling, as well as biological and antitumor activities screening. We have calculated and discussed the thermodynamics and protonation constants of TSC1 compound as a representative from the novel synthesized thiosemicarbazones. The solution speciation of different species was studied in accordance with pH. Molecular parameters of the optimized structures were calculated and discussed. The X-ray single crystal of TSC2 and TSC3 compounds have been established where TSC2 crystallizes in P21/c, a = 11.2343 (6) Å, b = 11.2575 (7) Å, c =11.8995 (8) Å, α = 90.00°, β = 94.476(7) °, γ = 90.0°, V = 1500.34 (16) Å3, Z = 4, however, TSC3 crystallizes in the space group P21/c, a = 27.958 (12) Å, b= 12.072 (5) Å, c = 9.833 (4) Å, α = 90.0°, β = 93.117(11) °, γ = 90.0°, V = 3486.75 Å3, Z = 7. Considering the antimicrobial activities and correlating structure-activity relationship for the synthesized compounds, TSC1 molecule behaves as a promising candidate as an antifungal agent versus Candida albicans. Consequently, that would be very helpful in the field of medicinal chemistry especially as antimicrobial agents. The results are of vital significance to the chemistry of antimicrobial agents.

Express method for determining the mass fraction of table salt in hard cheeses

The process of pickling cheeses is an important industrial operation that actively affects proteolytic transformations with a ripening of cheese mass. The correction of the mass fraction of table salt in cheese mass allows adjusting the activity of the development of lactic acid microorganisms of a starter in it, which greatly affects the formation of sensorial, physical and chemical parameters of the finished product. Determination of the mass fraction of the table salt is an integral part of techno-chemical control of cheese production and requires significant promptness. Standardized methods for determining the mass fraction of the table salt in cheese mass are associated with time consuming laboratory studies (“Method with the silver nitrate”, “Method with a cationite”, etc.). The method of determining the content of table salt in the cheese mass of hard cheeses, this method having been approved in the department of butter and cheese making of the Institute of Food Resources NAAS, is based on the results of potentiometric measurements with the subsequent calculation according to the empirical formula and is reliable and not time consuming

Adsorption of the Tartrate Ions in the Hydroxyapatite/Aqueous Solution of NaCl System

The research on the interaction of tartrate ions with the surface of hydroskyapatite was presented, including the measurements of the kinetics of tartrate ion adsorption and tartrate ion adsorption as a function of pH. The adsorption of tartrate ions was calculated from the loss of tartrate concentration in the solution as measured by a radioisotope method using C-14 labeled tartaric acid. In order to explain the mechanism of interaction of tartrate ions with hydroxyapatite, supplementary measurements were carried out, i.e., potentiometric measurements of the balance of released/consumed ions in the hydroxyapatite/electrolyte solution system, zeta potential measurements, FTIR spectrophotometric measurements and the hydroxyapatite crystal structure and particle size distribution were characterized. It was found that the adsorption of tartrate ions occurs as a result of the exchange of these ions with hydroxyl, phosphate and carbonate ions. Replacing the ions with the abovementioned tartrate ions leads to the appearance of a negative charge on the surface of the hydroxapatite. On the basis of XRD study and particle size distribution, a decrease in the size of crystallites and the diameter of hydroxyapatite particles in contact with a solution of 0.001 mol/dm3 of tartaric acid was found.

Study and evaluation antioxidant activity of dietary supplements with green tea extract

The aim of the work is to determine and evaluate the antioxidant activity of dietary supplements with green tea extract, as well as to introduce conditional terms of the level of AOA. Materials and methods. The object of the study was dietary supplements of different manufactures: “Green Tea Extract” of Natural Sources, USA (DS1), “Extract of green tea” of Elit-Pharm, Ukraine (DS2) and “Green tea” of Pharmakom, Ukraine (DS3). Potentiometric measurements were conducted by pH meter Hanna 2550 (Germany) with a combined platinum electrode EZDO 5010. Epigallocatechin-3-O-gallate ˃98.0 % (Sigma Aldrich), K3[Fe(CN)6], K4[Fe(CN)6], NaHPO4, KH2PO4 were analytical grade. Results. It was established that a value of the antioxidant activity of DS1 was 36.51 mmol/tab, DS2 – 29.78 mmol/tab, and DS3 – 16.67 mmol/tab. DS1 had the highest value of the antioxidant activity, which correlated with the content of catechins (r2 = 0.9314). According to the proposed conditional terms of antioxidant activity dietary supplements, DS1 and DS2 possessed a low level of antioxidant activity, whereas DS3 corresponded to very low level of antioxidant activity. Conclusions. It was found that the studied dietary supplements with green tea extract have antioxidant activity, which correlates with the content of catechins.

New perspective on the powers and limitations of potentiometric redox measurements, a possible game changer

<p>The redox potential (Eh) is a master variable affecting speciation and fate of nutrients and pollutants in aqueous environments. To date, direct potentiometric measurements using redox electrodes are the only viable means of monitoring Eh in-situ and continuously. While some scholars indicated the quantitative value of this direct Eh measurement, many have argued that because there are often discrepancies between the measured Eh and the measured speciation of redox active species in solution, the electrode measurements can be regarded as qualitative at best. The ambiguity regarding the quantitative power of potentiometric Eh measurements has led many to disregard this important analytical tool. The question is raised – are there environments in which redox electrodes give a more reliable representation of the redox state than others? We investigated this question in a simplified system of solubilized Fe in different concentrations and various ratios of FeCl<sub>3</sub> to FeSO<sub>4</sub>. HCl and KCl were added to achieve different pH value (in the range of 2-4) and ionic strength levels (10-100 mM). The solutions were maintained stirred and were monitored continuously and simulatenously using 7 permanently installed redox electrodes with a data logger. The electrode readings were compared with the Eh calculated by external measurement of Fe speciation and the known solution inputs. In the initial solution, where only the ferrous iron form was added, a standard deviation of ~10mV was found between the electrodes used in this study; additions of Ferric iron to these solutions led to a decrease in standard deviation between electrodes down to ~2mV and concurrently to a convergence between electrode readings and the Nernst-based calculated Eh. The increased deviation in low ferric iron concentrations occurred regardless of the measuring device or if an external reference electrode was used. These findings suggest that potentiometric measurements have an effective range for which they can be used, which has been widely overlooked in the literature.  We examined different indices to define the effective range. Using the standard deviation as the index of the effective range, it was determined that in the tested solutions deviations increased when Fe<sup>+3 </sup>molar activity was <20 nM at an ionic strength of 10-20mM; but the rise occurred at a lower value (<5nM) in solutions with ionic strength ~100mM. The increased effective range at higher ionic strength points towards electron shuttling as a possible effector of the electrode range; if so, it is postulated that in natural systems, electron shuttling by organic matter may greatly increase electrode effective range. We believe that once the understanding that potentiometric redox measurements have an effective range is further established and explored it may be a game changer which will promote both the development of methods to define the effective range and technical improvements to increase electrode effective range so that potentiometric redox measurements can be more widely utilized as a quantitative tool.</p>

4,4′-Isopropylidenebis(2,6-dibromophenol) Photocatalytic Debromination on Nano- and Micro-Particles Fe3O4 Surface

Background: Tetrabromobisphenol A (4,4’-isopropylidenebis(2,6-dibromophenol), TBBPA) is one of the most widely used brominated flame retardants. Due to its widespread use, high lipophilicity, and persistence, it has been detected in various environmental samples. Therefore, it is of great significance to develop methods to efficiently remove TBBPA from the contaminated environment. Objective: The aim of our study was to examine photocatalytic dehalogenation of TBBPA on microand nano-sized Fe3O4 exposed to the visible light. The Fe3O4 catalyst was chosen due to its indisputable low impact on the environment. Methods: A solution of TBBPA (1.84 × 10-4 mol dm-3) with a pH = 8 with suspended catalyst was illuminated (light intensity about 1.1x1017 photons per second, spectrum range 200-600 nm) for 1 hour. Analysis of the reaction progress was carried out by HPLC measurements of TBBPA decay and potentiometric measurements of an increase in bromide concentration. Results: The degradation process seems to be the most effective for TBBPA in the reaction mixture containing the n-Fe3O4 (t0.5 ≈ 2 min). Slightly lower degradation efficacy is observed for TBBPA degradation in the presence of the μ-Fe3O4 (decay within the first 5 min). TBBPA decomposition of both n-Fe3O4 and μ-Fe3O4 is accompanied by different bromide concentrations time-profile. Conclusion: The photogenerated electron-induced degradation by dissociative-attachment to the aromatic ring was followed by bromine ion expulsion. The micro-magnetite showed a strong tendency for adsorption of bromide anions during the process, which could be adventurous for the overall waste-decontamination process.