Potentiometric Techniques Research Articles

Thermodynamic Study of (KCl + N,N-Dimethylformamide + Water) System Based on Potentiometric Measurements

In this research, the thermodynamic properties of (KCl + N,N-dimethylformamide + water) system were determined based on potentiometric technique. The electromotive force measurements were carried out by using self-made electrodes on the galvanic cell of type Ag|AgCl|KCl (m), N,N-dimethylformamide (w), and H2O (1 – w)|K-ISE in various mass fractions of N,N-dimethylformamide in water (0, 0.10, 0.20, and 0.30) in the molality ranging from 0.0094 to 2.5200 mol·kg–1 at T = (298.2 and 308.2) K and P = 0.1 MPa. Thermodynamic properties modeling was implemented using the Debye–Huckel extended equation, Pitzer ion interaction, and Pitzer–Simonson–Clegg models. Subsequently, unknown parameters for each model were determined and utilized to calculate the thermodynamic properties such as the mean activity coefficients, the osmotic coefficients, the excess Gibbs free energy, and the solvent activity for the system under investigation.

Equilibrium studies of diethyltin(IV) dichloride and divinyltin(IV) dichloride with 1-(2-aminoethyl)-pyrrolidine

The interaction of diethylltin(IV) (DET) and divinyltin(IV) (DVT) with 1-(2-aminoethyl)-pyrrolidine (AEPY) was investigated using potentiometric technique at ionic strength of 0.1 mol dm−3 NaNO3. The hydrolysis constants of diethyltin(IV) and divinyltin(IV) cations and the stepwise formation constants of the complexes formed in solution were calculated at different temperatures and in solutions of dioxane-water solutions of different compositions. The stoichiometry and stability constants for the complexes formed were reported. The results showed the formation of 1:1 complex and the corresponding hydroxo complexes. The concentration distributions of the various complex species were evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants were investigated for DET and DVT complexes with AEPY. The equilibrium constant for the displacement of 1-(2-aminoethyl)-pyrrolidine coordinated to diorganotin(IV) by thymine and thymidine as representative examples of DNA constituents was calculated from calculations based upon equilibrium properties. The results are expected to contribute to the chemistry of tin(IV) based anticancer agents.

Salicylamide derivatives for iron and aluminium sequestration. From synthesis to complexation studies

This paper presents an easy, fast and economic synthesis of chelating agents for medical, environmental and analytical applications, and the evaluation of the stability of their complexes with Fe3+ and Al3+. Complex formation equilibria with Cu2+ and Zn2+ metal ions were also studied to evaluate if the chelating agents can perturb the homeostatic equilibria of these essential metal ions. Effective chelating agents for metal ions, in addition to their well-known medical uses, find an increasing number of applications in environmental remediation, agricultural applications (supplying essential elements in an easily available form), and in analytical chemistry as colorimetric reagents. Besides the stability of the complexes, the lack of toxicity and the low cost are the basic requisites of metal chelating agents. With these aims in mind, we utilized ethyl salicylate, a cheap molecule without toxic effects, and adopted a simple synthetic strategy to join two salicylate units through linear diamines of variable length. Actually, the mutual position of the metal binding oxygen groups, as well as the linker length, affected protonation and complex formation equilibria. A thorough study of the ligands is presented. In particular, the complex formation equilibria of the three ligands toward Fe3+, Al3+, Zn2+ and Cu2+ ions were investigated by combined potentiometric and spectrophotometric techniques. The results are encouraging: all the three ligands form stable complexes with all the investigated metal ions, involving the oxygen donor atoms from the 2-hydroxybenzamido unit, and nitrogen atoms in copper and zinc coordination.

Sequential and Selective Detection of Two Molecules with a Single Solid-Contact Chronopotentiometric Ion-Selective Electrode.

A polymeric membrane ion-selective electrode (ISE) is typically designed for the determination of one specific ion using a conventional method. In this work, we demonstrate a simple, versatile, and sensitive platform for simultaneous detection of two molecules with a single ISE. Under a series of periodic galvanostatic polarization, a solid-contact ISE without ion exchanger properties under zero-current conditions has been successfully used for simultaneous detection of two opposite charged ions with high sensitivity, good selectivity, and fast reversibility. By integration of biorecognition elements with the potentiometric measurement, highly sensitive and selective detection of a broad range of different molecular targets can be predicted. As a proof of concept, a potentiometric genosensor based on magnetic beads-enzyme sandwich assay has been designed for sensitive and selective detection of pathogenic bacteria Escherichia coli O157:H7 and Staphylococcus aureus. Under optimal conditions, two bacteria nucleic acid sequences can be detected simultaneously with high sensitivity and good selectivity by using a single solid-contact potentiometric ISE. The detection limits of Escherichia coli O157:H7 DNA and Staphylococcus aureus DNA are 120 and 54 fM (3σ), respectively. Because of its simplicity, this potentiometric technique based on ISE can be an attractive tool or detector to perform two analyte measurements.

New Method for Simultaneous Determination of Ascorbic and Acetylsalicylic Acids in Effervescent Tablets

The determination of the real concentration in different pharmaceutical drugs represents a very important goal of the pharmaceutical industry. The main aim of the study was to set up a simple, cheap and rapid method in order to determine both ascorbic and acetylsalicylic acid content of effervescent tablets that could be found on the pharmaceutical market, without preliminary separation or extraction. For this purpose, a very simple and reliable clock method based on two Landolt-type systems of reactions, based on potentiometric techniques, has been developed. The method has been tested on different effervescent tablets which contain ascorbic acid and acetylsalicylic acid in different mixture ratio.

Measurement and thermodynamic analysis of the acid-base equilibria of two bioactive flavanone glycosides in different temperatures and non-aqueous mixtures

In this research, the acid-base properties of two glycosilated flavanones namely naringoside and hesperidin were thermodynamically studied using spectrophotometric and potentiometric techniques at various temperatures (293.15–313.15) K. Because of very low solubility of these flavanones in aqueous solution, the protonation constants were obtained in ethanol-water mixtures (60–90% v/v) containing 0.10moldm−3 tetra-n-butylammonium perchlorate (TBAP) as supporting electrolyte for naringoside and DMSO-water mixed solvents (50–95% v/v) containing 0.10moldm−3 NaCl for hesperidin. Data process for the calculation of the protonation constants was done using the computer program STAR. The thermodynamic quantities (ΔG°, ΔH°, and ΔS°) of the protonation process were obtained by means of modified van't Hoff equation. It was found that the acid dissociation reaction is exothermic and the entropic contribution is low for both the flavanones. Finally, the influence of solute-solvent interactions on the protonation equilibria in various temperatures was modelled using Kamlet, Abboud and Taft (KAT) solvatochromic parameters and Hildebrand's solubility index.

Introduction to Validation of Analytical Methods: Potentiometric Determination of CO2

Validation of analytical methods is a fundamental subject for chemical analysts working in chemical industries. These methods are also relevant for pharmaceutical enterprises, biotechnology firms, analytical service laboratories, government departments, and regulatory agencies. Therefore, for undergraduate students enrolled in majors in the field of chemistry, learning validation of methods and chemometrics is essential. The following article presents the development of a laboratory experiment to validate a method to determine CO2 by means of potentiometry. This experiment will allow students to approach a subject that may be part of their professional activities. The validated method was applied to determine CO2 in commercial carbonated beverages. A teaching activity on method validation was proposed and implemented for senior students. After its application, students were able to improve significantly their knowledge on the topic. The potentiometric technique, underlying the validated method, has the ad...

Staphylococcus aureus exotoxin detection using potentiometric nanobiosensor for microbial electrode approach with the effects of pH and temperature

ABSTRACTConsidering the ever-increasing population and trends in industrialization, it is difficult to detect the toxins produced in food products using traditional techniques. In this study, a potentiometric nanobiosensor technique using selective patterns for Staphylococcus aureus exotoxin was thoroughly considered. A molecular framework and polymer were produced using methacrylic acid (MAA) monomers, which formed covalent bonds between MAA monomers to produce a white polymer. In addition, hydrogen bonds formed between the amino acids of the exotoxin and the MAA functional groups, which functioned as selective sites for the polymer. To evaluate the effect of pH on the S. aureus exotoxin nanobiosensor, diluted solutions of NaOH and HNO3 were applied for the upper and lower pH levels, respectively. The effect of temperature was tested using distilled water at fixed temperatures. The results showed that the molecular framework polymer (MFP) in the designed biosensor was able to detect an exotoxin density up to 10–3 M at 68 nm of synthesized molecularly imprinted polymer (MIP) during the first 32 days of the experiment (from a total of 56 days). The potential differences remained constants at an optimum pH range of 5.0–8.5 and at an optimum temperature range of 15°C–25°C. Therefore, we concluded that the pH and temperature can affect the precision of a potentiometric nanobiosensor for detecting S. aureus exotoxin.

Solid Electrolyte Gas Sensor Based on a Proton-Conducting Graphene Oxide Membrane.

Graphene oxide (GO) is an ultrathin carbon nanosheet with various oxygen-containing functional groups. The utilization of GO has attracted tremendous attention in a number of areas, such as electronics, optics, optoelectronics, catalysis, and bioengineering. Here, we report the development of GO-based solid electrolyte gas sensors that can continuously detect combustible gases at low concentrations. GO membranes were fabricated by filtration using a colloidal solution containing GO nanosheets synthesized by a modified Hummers’ method. The GO membrane exposed to humid air showed good proton-conducting properties at room temperature, as confirmed by hydrogen concentration cell measurements and complex impedance analyses. Gas sensor devices were fabricated using the GO membrane fitted with a Pt/C sensing electrode. The gas-sensing properties were examined by potentiometric and amperometric techniques. The GO sensor showed high, stable, and reproducible responses to hydrogen at parts per million concentrations in humid air at room temperature. The sensing mechanism is explained in terms of the mixed-potential theory. Our results suggest the promising capability of GO for the electrochemical detection of combustible gases.

Liquid-phase synthesis of isoprene from MTBE and formalin using cesium salts of silicotungstic acid

A single-stage synthesis of isoprene from methyl tertiary-butyl ether (MTBE) and formalin in an organic-aqueous two-phase system were studied by using Cs-exchanged silicotungstic acid catalysts (CsXH4-XSiW12O40, abbreviated as CsX-STA). The CsX-STA catalysts (x=2.0, 2.5, 3.0, and 3.5) were prepared using Cs2CO3 as Cs source and water as solvent. The catalysts were characterized by using XRF, FTIR, FT-Raman, XRD, N2 sorption, light scattering, TGA, and potentiometric titration techniques to relate catalytic activities to catalyst properties. The characterization results showed that the Keggin structure and cubic unit cell of all Cs-STA catalyst samples were well preserved. The increase in acid strength and total acid sites with decreasing Cs content (x) resulted in increasing formaldehyde conversion and isoprene selectivity. However, at low Cs content (x≤3.0), the high contribution of homogeneous catalysis also played a role in the catalytic activities. The highest activity (isoprene formation normalized with total acid sites) of Cs2.5-STA catalyst was found to be attributed to its high surface area. For the organic solvent effect, the Cs2.5-STA catalyst activity increased with the increasing solvent polarity in the order: n-hexane < cyclohexane < toluene.

Nickel(II), zinc(II) and cadmium(II) complexes of peptides containing separate aspartyl and cysteinyl residues

Nickel(II), zinc(II) and cadmium(II) complexes of two hexapeptides ADAAAC-NH2 and AADAAC-NH2 containing terminal amino, separate aspartyl carboxylate and cysteinyl thiolate donor functions have been studied by potentiometric and spectroscopic techniques. For nickel(II), the amino terminus and the aspartyl residues are the primary metal binding sites. At high pH values, thiolate groups can also coordinate to nickel(II) and this interaction results in the co-existence of various coordination isomers. In the case of AADAAC-NH2, even dinuclear complexes can be formed with separate (NH2, N−, N−, COO−) and (S−, 3N−) binding modes. On the contrary, the thiolate functions are the primary binding site for zinc(II) and especially cadmium(II) ions. The formation of macrochelate complexes is the most characteristic with these metal ions including the terminal amino, the internal carboxylate and thiolate donor functions. None of the side chain donors can, however, induce the deprotonation and zinc(II) or cadmium(II) coordination of the amide functions of these peptides.

Physicochemical properties and antimicrobial activity of new spirocyclic thieno[2,3-d]pyrimidin-4(3H)-one derivatives

A number of 6'-methylidene-2,3-dihydro-1H-spiro[pyridine-4,5'-thieno[2,3-d]pyrimidin]-4'(3'H)-one derivatives, obtained as major products of a domino reaction between 5,6,7,8-tetrahydropyrido[4',3':4,5]thieno[2,3-d]pyrimidines and electron-deficient alkynes, were characterized for their acid-base properties and lipophilicity and evaluated for the antimicrobial activity against a number of clinical isolates of bacterial and fungal strains. The cytotoxicity against four tumor cell lines was also screened for some compounds. The dissociation constants (pK a) and partition coefficients (log P) in 1-octanol–water system were determined using a potentiometric technique. The negative difference between the observed and calculated log P values could be explained in the light of the conformational rigidity. Most of the studied compounds showed a moderate and selective activity against Gram-positive bacteria strains (S. agalactiae, E. faecalis, S. epidermidis), whereas did not exhibit any effect against Gram-negative bacteria and fungi at the maximum test concentration (500 μM). Implications of the physicochemical properties in modulating the antimicrobial activity and cytotoxicity of the examined spirocyclic thieno[2,3-d]pyrimidin-4(3H)-one derivatives are also discussed.

Esterification of oleic acid to biodiesel over a 12-phosphotungstic acid-based solid catalyst

A 12-phosphotungstic acid (PTA)-based esterification catalyst was prepared by modifying PTA with 1,2,3-trizaole-4,5-dicarboxylic acid (TDA). The obtained TDA-PTA sample was characterized with XRD, IR, SEM, TG and potentiometric titration techniques, and its catalytic properties for esterification of oleic acid with methanol were studied. In addition, the effects of reaction conditions, including catalyst amount, oleic acid/alcohol molar ratio, reaction time and reaction temperature, on its catalytic performance were investigated. After modification with TDA, although the Keggin structure of PTA is kept and the sample shows strong acidity, the particle morphology changes to regular spheres. In particular, the sample exhibits high catalytic activity and stability in esterification of oleic acid with methanol. The modification of PTA by TDA effectively prevents PTA from dissolving in the reaction mixture, and thus, the TDA-PTA can be recycled at least six runs without severe loss of catalytic activity, showing that it is a good heterogeneous catalyst for esterification.

Thermodynamic, Spectroscopic, and Computational Studies of f-Element Complexation by N-Hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic Acid.

Potentiometric and spectroscopic techniques were combined with DFT calculations to probe the coordination environment and determine thermodynamic features of trivalent f-element complexation by N-hydroxyethyl-diethylenetriamine-N,N',N″,N″-tetraacetic acid, HEDTTA. Ligand protonation constants and lanthanide stability constants were determined using potentiometry. Five protonation constants were accessible in I = 2.0 M (H+/Na+)ClO4. UV-vis spectroscopy was used to determine stability constants for Nd3+ and Am3+ complexation with HEDTTA. Luminescence spectroscopy indicates two water molecules in the inner coordination sphere of the Eu/HEDTTA complex, suggesting HEDTTA is heptadentate. Luminescence data was supported by DFT calculations, which demonstrate that substitution of the acetate pendant arm by a N-hydroxyethyl group weakens the metal-nitrogen bond. This bond elongation is reflected in HEDTTA's ability to differentiate trivalent actinides from trivalent lanthanides. The trans-lanthanide Ln/HEDTTA complex stability trend is analogous to Ln/DTPA complexation; however, the loss of one chelate ring resulting from structural substitution weakens the complexation by ∼3 orders of magnitude. Successful separation of trivalent americium from trivalent lanthanides was demonstrated when HEDTTA was utilized as aqueous holdback complexant in a liquid-liquid system. Time-dependent extraction studies for HEDTTA were compared to diethylenetriamine-N,N,N',N″,N″-pentaacetic acid (DTPA) and N-hydroxyethyl-ethylenediamine-N,N',N'-triacetic acid (HEDTA). The results indicate substantially enhanced phase-transfer kinetic rates for mixtures containing HEDTTA.

Erratum to: Interactions of N′-[1-(2-Hydroxyphenyl)ethylidene] Isonicotinohydrazide, a Hydrazone Schiff Base and Selected Lanthanides: Potentiometric and Spectral Studies

Potentiometric and spectroscopic techniques are used to study the interaction of N′-[1-(2-hydroxyphenyl)ethylidene]Isonicotinohydrazide (HpEH) with trivalent Pr, Nd, Gd, Tb, and Ho ions. Potentiometric titrations, carried out keeping the Ln3+/HpEH molar ratios at 1:2 and 1:4 at different temperature and a constant ionic strength of 0.1 mol·dm−3 KNO3 in aqueous dioxane (40%) medium, show two protons of the ligand in equilibrium and complex formation of 1:1, 1:2 and 1:3 Ln3+/HpEH stoichiometry. The conditional stability constants of the Ln3+–HpEH complexes increase in the order: Pr < Nd < Gd < Tb < Ho. The negative values of the standard state thermodynamic parameters (ΔG°, ΔH°, and ΔS°) associated with both protonation and complexation reactions for all the systems show the reactions are spontaneous, exothermic and of unfavorable entropy. Changes in the absorption bands indicate interactions of HpEH and Ln3+. Photoluminescence study of the Tb3+ and HpEH complex reveals that HpEH is florescent and has no sensitizing effect on Tb3+ luminescence in ethanol, while in the isolated solid Tb3+–HpEH complex the luminescence intensity was found to be greatly sensitized. The synthesized Tb3+–HpEH complex, characterized on the basis of elemental analysis, magnetic susceptibility, molar conductivity, thermal analysis and spectral measurements is paramagnetic, acts as a 2:1 electrolyte and is of 1:3 Ln3+/HpEH stoichiometry.

Metal Sulfide-Blended Sulfur Cathodes in High Energy Lithium-Sulfur Cells

Lithium-sulfur cells exhibit poor cycle life, due to the well-known ‘polysulfide shuttle’ enabled by the dissolution of the sulfur reduction products in organic electrolyte. Different strategies have been implemented to reduce the shuttle effects, with limited success, especially through use of low sulfur loadings (1–2 mg/cm2). Dense electrodes with high sulfur loadings are essential for high energy cells, however, such electrodes experience more serious polysulfide effects. In this paper, we describe the benefits of blending sulfur with a transition metal sulfide (here, TiS2 and MoS2) to form dense composite cathodes with enhanced conductivity. There is an improvement in both the initial capacity from sulfur utilization (∼800 mAh/g based on sulfur content), the coulombic efficiency (>96%) and also in cycle life upon blending with the metal sulfide. High sulfur loadings (>12 mg/cm2 or ∼6 mAh/cm2 per side) were demonstrated to display high sulfur utilization in Li-S cells containing the metal sulfide blends either with or without coatings over the sulfur cathode. XRD studies were carried out to understand the redox behavior of the metal sulfide additive during charge/discharge cycling of the sulfur cathodes. DC polarization and Potentiometric Intermittent Titration Technique (PITT) measurements were made on sulfur cathodes with and without metal sulfide blends to determine the charge transfer and diffusional kinetics.

Complexation studies of N′-[(1E)-1-phenylethylidene]isonicotinohydrazide: An aroylhydrazone Schiff base and lanthanides

The interaction of N′-[(1E)-1-phenylethylidene]isonicotinohydrazide (PHeH) with trivalent Pr, Nd, Gd, Tb, and Ho ions was studied with spectroscopic and potentiometric techniques. Photoluminescence studies of Tb3+ and PHeH in ethanol and in solid Tb3+-PHeH complex reveal that PHeH has no sensitizing effect on Tb3+ luminescence. The absorption spectral bands of PHeH under different conditions and that of Nd3+- PHeH at different molar ratios were investigated. Potentiometric titrations of 1:4 Ln/PHeH molar ratio carried out at different temperature at a constant ionic strength of I=0.1mol·dm−3 KNO3 in aqueous-dioxane medium reveal the moderate thermodynamic stability constants of the complex formation equilibria which follow the order: Pr<Nd<Gd<Tb<Ho. The thermodynamic parameters (ΔG, ΔH, and ΔS) of protonation and complexation reactions are all negative suggesting the spontaneous, exothermic, of unfavorable entropy and enthalpy-driven reactions. Actual synthesis and characterization of Tb3+-PHeH complex, confirmed the veracity of the complex formation equilibria. Finally, the information accrued from the studies is used in the structural elucidation of the complexes.

Spectrofluorimetric and Potentiometric Determination of Acidity Constants of 4-(4'-Acetyloxy-3'-Methoxybenzylidene)-5-Oxazolone Derivatives.

4-(4'-acetyloxy-3'-methoxybenzylidene)-5-oxazolone fluorescent molecules bearing four different aryl groups attached to the 2-position of 5-oxazolone ring have been investigated by spectrophotometric and potentiometric techniques in solution media. The acidity constants (pKa) of the fluorescent molecules were precisely determined in acetone, acetonitrile, dimethylformamide and in 1:1 mixture of toluene-isopropanol. The studied derivatives were titrated with tetrabutylammonium hydroxide and non-aqueous perchloric acid by scanning the basic and acidic region of the pH scale. A computerizable derivative method was used in order to descript precisely the end point and pKa values. The molecules investigated performed well-shaped and stoichiometric potentiometric titration curves.

Coordination Chemistry and f-Element Complexation by Diethylenetriamine-N,N″-bis(acetylglycine)-N,N',N″-triacetic Acid.

Potentiometric and spectroscopic techniques were used to evaluate the coordination behavior and thermodynamic features of trivalent f-element complexation by diethylenetriamine-N,N″-bis(acetylglycine)-N,N',N″-triacetic acid (DTTA-DAG) and its di(acetylglycine ethyl ester) analogue [diethylenetriamine-N,N″-bis(acetylglycine ethyl ester)-N,N',N″-triacetic acid (DTTA-DAGEE)]. Protonation constants and stability constants of trivalent lanthanide complexes (except Pm3+) were determined by potentiometry. Six protonation sites and three metal-ligand complexes [ML2-, MHL-, and MH2L(aq)] were quantified for DTTA-DAG. Four protonation sites and one metal-ligand complex [ML(aq)] were observed for DTTA-DAGEE, consistent with the presence of two ester groups. Absorption spectroscopy was utilized to measure the stability constants for complexation of trivalent neodymium and americium by DTTA-DAG and trivalent neodymium by DTTA-DAGEE. The coordination environment of trivalent europium in the presence of DTTA-DAG was investigated at various acidities by luminescence lifetime measurements. Decay constants indicate one water molecule in the inner coordination sphere across the 1.0 < pH < 5.5 range, presumably due to octadentate coordination by DTTA-DAG. A trans-lanthanide pattern of complex stabilities for DTTA-DAG was found to be analogous to that observed for DTPA, with a ∼106 reduction of the complex stability. The lessened strength of complexation, relative to DTPA, was attributed to significant reduction of the total ligand basicity for DTTA-DAG due to the electronic influence of amide functionalization. When DTTA-DAG is used as an aqueous holdback complexant in liquid-liquid distribution experiments, the preferential coordination of Am3+ in the aqueous environment offers efficient An/Ln differentiation. The separation extends to pH 2 conditions, where the kinetics of phase transfer in such liquid-liquid systems are aided by the acid-catalyzed dissociation of a metal/aminopolycarboxylate complex.

Fac‐[Re(H2O)3(CO)3]+ Complexed with Histidine and Imidazole in Aqueous Solution: Speciation, Affinity and Binding Features

AbstractThe use of isotopes of transition metal has opened many perspectives in the development of novel compounds utilizable for therapeutic or diagnostic purposes. In order to be exploited, though, they must be stabilized by chelating systems in coordination complexes. The tricarbonyl complexes of Technetium(I) and Rhenium(I) have assumed important roles in these fields as they are readily conjugated to biomolecules to form stable probe useful in the targeting approach. In this context the amino acid histidine represents a valuable ligand for bioconjugation. Since little is reported on the chemistry and speciation of Re(I) and Tc(I) in aqueous solution, here, we analyze the interaction of fac‐[Re(H2O)3(CO)3]+ with histidine or with the simple imidazole ring by means of potentiometric and spectroscopic techniques. We describe in details the equilibria that arise in solution, calculate the constants of each equilibrium reaction and report coordination properties and atomic details of the formed complexes. Our data represent a valuable contribute towards the exploitation in nuclear medicine of histidine containing biomolecules complexing Tc (I) and Re(I).