Potentiometric Titration Technique Research Articles

A novel approach to study ascorbic acid oxidation using hexavalent chromium species—theoretical and practical perspectives of the use of potentiometric titration technique

AbstractThis paper highlights the advantages of using the potentiometric titration technique as a valuable tool for studying the oxidation reaction of ascorbic acid by hexavalent chromium species in aqueous solutions. Particular attention was paid to the method of determining diagnostic points allowing the quantification of ascorbic acid in the sample under study. Additionally, the influence of experimental conditions, specifically the pH of the system and the concentration of the reactants, on the type of hexavalent chromium species involved in the interaction with ascorbic acid was analyzed. It has been shown that the method presented provides a simple, cost-effective, and rapid tool that can be widely used for the direct determination of ascorbic acid.

Enhancement in Anticancer Activity of Chitosan Tailored Imidazole-2-Thiosemicarbazones against MCF-7 Cancer Cell Line by Coordination with Copper(II) Ions

The coordination behavior of new batch synthesized chitosan imidazole-2-thiosemicarbazones tailored from both the low molecular weight commercial chitosan and high molecular weight crab shell chitosan was confirmed by Fourier Transform Infrared (FT-IR) and magnetic susceptibility measurements. Chlorine content in the complexes was estimated by potentiometric titration technique. The study showed the tridentate NNS tridentate coordination with copper (II) ion in a square planar orientation with the remaining valence satisfied by coordination with chloride ion. The MTT assay studies showed an enhancement in the anticancer activity of these chitosan thiosemicarbazone ligands upon their coordination with copper (II) ions against the human breast cancer (MCF-7) cell line in vitro. The minimal cytotoxicity of both the ligands and complexes against the normal mouse embryonic fibroblast (NIH3T3) cells revealed the selective attraction of these biomaterial chitosan derivatives towards the cancer cells with non-toxicity to healthy cells. There was only a marginal effect of molecular weight (Mw) and degree of deacetylation (DDA) of chitosan upon the anticancer activity of these chitosan derivatives.

Application of a modern theoretical approach to the study of the interaction of KR-12 peptides derived from human cathelicidins with Cu(II) ions.

The human cationic antimicrobial protein (hCAP) corresponding to the overlapping sequences of 151-162 of hCAP named KR-12 peptide is the smallest portion of the only type of human Cathelicidin, which has been shown to be modifiable into a more effective antimicrobial. In this study, an in silico analysis, supported by potentiometric titration and isothermal titration calorimetry techniques, was performed to identify potential Cu(II) binding sites of KR-12. The analysis of the presented data at the given theoretical level (GFN2-xTB/ALPB) revealed which peptide chain fragments are involved in the most favourable KR-12-Cu(II) binding mode. Based on a quantum chemical approach, the most favourable coordination modes of Cu(II) to peptides are proposed together with the discussion of the chemical nature of the interactions. The presented results demonstrated that KR-12 interacts with metal ions mostly via the main chain's oxygen atoms; however, the two types of amino acids that are expected to be vital for the interaction of Cu(II) are D (aspartic acid) and R29 (arginine). It was demonstrated that in order to explain the complexity of the interaction process in peptide-metal ion systems, the use of theoretical methods is sometimes necessary to explain the details of the experimental results and provide an in-depth understanding of these dynamic systems.

(Best Student Presentation) A Calorimetric and Potentiometric Titration Method to Elucidate Ca2+ Solvation Thermodynamics

Calcium metal batteries are a promising long-term sustainable alternative to lithium metal batteries due to calcium’s high natural abundance and low electrochemical redox potential. Learning how to control Ca2+ coordination chemistry is essential in enabling high performance and stable calcium batteries. While several spectroscopic and computational studies of Ca2+ coordination have been conducted, they are limited by their qualitative nature and/or require experimental validation. This work introduces a novel methodology using a combination of calorimetric and potentiometric titration techniques, to quantitatively probe electrolyte coordination shell composition, as well as previously unattainable experimental coordination enthalpy, Gibbs free energy, and entropy. To establish the effectiveness of the method, here we investigate the coordination shell thermodynamics in simpler, highly dissociating LiPF6 electrolytes. Starting with a weakly solvated electrolyte, we titrate in a strong solvent—which preferentially coordinates to Li+—and measure the associated heat release/absorption and Li+ potential change with each injection. Fitting both sets of data to a mathematical binding model allows for the extraction of the change in enthalpy (ΔHi), Gibbs free energy (ΔGi), and entropy (ΔSi) associated with each Li+-solvent complex formation. Several weak solvent and strong solvents are investigated to build a dataset of ΔHi, ΔGi, and ΔSi. These thermodynamic values are used to calculate the average coordination number of each solvent in the Li+ coordination shell which agree well with literature. Raman and NMR spectroscopy confirm salt dissociation and solvent displacement during titration. This method unlocks a precise description of the chemical environment around Li+ and enables prediction of the Li+ coordination shell in new electrolytes by rationalizing the hierarchy of solvent binding. Given that this method extends to relevant calcium electrolytes, it is a powerful tool to engineer effective electrolytes for use with a calcium metal anode.

Relative stability and species formation of Zn(II) ternary complexes involving L-Tryptophan, L- Citrulline, L-Glutamine with biologically active nulceobases Uracil and Thymine in solution

Binary and ternary complexes of Zn(II) metal ions were prepared with the two nucleobases viz. Thymine and Uracil in a stoichiometric ratio of 1:1 and 1: 1:1 (Mn+: L), where Mn+ =Zn2 + and L = ligand (A) Amino acids (aa) L-Tryptophan, L- Citrulline, L-Glutamine and B = nulceobases : Uracil and Thymine in aqueous solution at 37 ± 1 °C. All the experiments performed kept the ionic strength I = 0.1 mol dm-3 (NaNO3) and done by potentiometric titration technique. The stoichiometric ratios of the formed complexes were done by using molar ratio method. The protonation constants of the ligands and the stability constants of the binary and ternary complexes of Zn(II) with the ligands were calculated from the method suggested by Irving and Rossetti method. Computed data were obtained using the ‘‘SCOGS’’ computer program are more refined. Origin 6.0 program software program used to the get the species distribution diagrams of the species formed at different pH range. The mixed ligand ternary complexes showed simultaneous formation in most cases observed at high pH range. The gradual drop of the binary concentration showed the ternary specie formation in that pH range. Here, we have described the general equilibria of complexes, amount of species (%) formed and their relative stability of Zn(II) mixed ligand ternary complexes and order of stability of the ternary complexes with respect to ligands used.

Complex Equilibria and Distribution of Metal (II) Ions with Biologically Active Chelating Agents in Aqueous and Aqueous-organic Media

An understanding of the principles of complex equilibria and species distribution in different solutions is important in expounding and correlating the interaction of different ligands with different metal ions in complex formation. Therefore, acid-base equilibria involved in the formation of binary and ternary complexes of Co (II), Cu (II) and Pb (II) with methionine (Met) and uracil (Urc) have been determined by potentiometric titration technique. The stability constants of the complexes were evaluated at 35 ± 0.1°C and 0.02 M ionic strength (kept constant with NaNO3) in aqueous and organic-aqueous media. The species distribution in solutions as a function of pH was determined using the Hyss program. The stability of the ternary complexes relative to the corresponding binary complexes of the secondary ligand is measured in terms ΔlogK and % RS values. The ternary complexes are observed to be more stable than binary complexes in the media except for [CuMetUrc] ternary complex in organic-aqueous medium where the ternary complex is less stable than the binary complex of the uracil. The overall stability of the ternary complexes was higher in organic-aqueous system than aqueous system. The stability of the complexes was found to be correlated with the covalent index of the metal ions and Jahn Teller distortion. pH-studies of these systems revealed an increase in the concentrations of the ternary complexes with increase in pH. The formation of binary complexes was shown to be favoured in physiological pH range (3-7) while that of the ternary complexes is observed to be favoured in the pH range 5-10.

Determination of Stability Constants and Thermodynamic Parameters for Ciprofloxacin-HCl With Some Transition Metal Ions by Potentiometric Titration Technique

This study included calculating the stability constants and stoichiometries of some binary complexes formed from the interaction of seven of metal ions (Cr+3,Mn+2,Co+2,Ni+2,Cu+2,Zn+2 and Cd+2) with Ciprofloxacin-HCl. This study was carried out using Potentiometric Titration Technique at different concentrations of the drug and the metal ion and at temperatures (288,298,310,318 and 328 K±0.1) in aqueous solution. Although, there are many methods available to study the stability of metal-ligand complexes, pH-metric is most frequently used to determine the stability constants. Hence, (Calvin - Bjerrum pH-metric titration technique) as adopted by Irving–Rossotti was used to calculate of stability constants. The results of the concentration effect study showed that the formation of complexes were more stable in dilute solutions, and through study of the temperature effect it was concluded that the stability of the complexes can be increased with raising temperature, and the stability constants value obtained were used in the calculation of thermodynamic parameters 〖(S〗^o,H,〖G〗^o). The results of this study also showed that the ciprofloxacin tends to form two types of metal complexes in the solution (ML1),(ML2) and this indicates that the reaction ratio between the drug and the metal ion was (1:1) and (1:2)(M:L) respectively for all metal ions. These ratios depended on the nature of the ligand or the metal ion, and the stability of the complexes formed increases according to the following arrangement (Mn+ 2< Co+ 2< Ni+ 2< Cu+ 2> Zn+ 2) and this arrangement is compatible with Irving Williams’s arrangement for the stability of the elements.

Novel AlCl3@nano Fe3O4-SiO2: a benign multi-layer magnetite nanocatalyst for the three-component one-pot synthesis of spiro[benzochromeno [2,3-d]pyrimidin-indolines

In this paper, sublimated AlCl3 has been embedded on nanosilica-Fe3O4 core via a simple method to obtain novel AlCl3@nano Fe3O4-SiO2 nanostructure for the first time. The newly synthesized solid has been characterized by Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDAX), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Brunauer-Emmett-Teller (BET) measurements, and potentiometric titration techniques. The reactivity of the prepared nanoparticles was investigated in the synthesis of spiro[benzochromeno[2,3-d]pyrimidin-indolines] through the one-pot three-component condensation of different naphthols, isatin derivatives, and barbituric acids in the in refluxing ethanol successfully. The recovery and reusability of the nanostructure has also been examined within 4 runs without activity loss.

Dipeptides of S-Substituted Dehydrocysteine as Artzyme Building Blocks: Synthesis, Complexing Abilities and Antiproliferative Properties

Background: Dehydropeptides are analogs of peptides containing at least one conjugate double bond between α,β-carbon atoms. Its presence provides unique structural properties and reaction centre for chemical modification. In this study, the series of new class of dipeptides containing S-substituted dehydrocysteine with variety of heterocyclic moieties was prepared. The compounds were designed as the building blocks for the construction of artificial metalloenzymes (artzymes). Therefore, the complexing properties of representative compounds were also evaluated. Furthermore, the acknowledged biological activity of natural dehydropeptides was the reason to extend the study for antiproliferative action of against several cancer cell lines. Methods: The synthetic strategy involves glycyl and phenylalanyl-(Z)-β-bromodehydroalanine as a substrate in one pot addition/elimination reaction of thiols. After deprotection of N-terminal amino group the compounds with triazole ring were tested as complexones for copper(II) ions using potentiometric titration and spectroscopic techniques (UV-Vis, CD, EPR). Finally, the antiproliferative activity was evaluated by sulforhodamine B assay. Results and Conclusions: A simple and efficient procedure for preparation of dipeptides containing S-substituded dehydrocysteine was provided. The peptides containing triazole appeared to be strong complexones of copper(II) ions. Some of the peptides exhibited promising antiproliferative activities against number of cancer cell lines, including cell lines resistant to widely used anticancer agent.

Equilibria Studies on Nickel(II) Complexes with 1,10-Phenanthroline Derivatives and Some Amino Acids in Aqueous Solution

In recent years, an increase in the biological applications of metal complexes of biologically active ligands has been observed due to their key role in clinical treatments. A potentiometric titration technique has been used to determine the protonation constants of biologically active ligands {glycine (gly), leucine (leu), methionine (met), phenylalanine (phe), tryptophan (trp), asparagine (asn), glutamine (gln), 1,10-phenanthroline (phen), 4-methyl-phenanthroline (4-mphen), 5-methyl-phenanthroline (5-mphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-tmphen), 5-nitro-phenanthroline (5-nphen)} and the stability constants of their (1:1) and (1:1:1) complexes with Ni(II) ion (I = 0.100 mol·L–1 KCl and T = 298.15 K). The protonation constants of the biologically active ligands and the stability constants of the (1:1) and (1:1:1) complexes of Ni(II) with the biologically active ligands have been computed by using the BEST program. Moreover, the SPE program has been used to determine the distribution of the species that occurred in the aqueous solution medium. The relative stabilities of the (1:1:1) Ni(II) complexes are compared with those of the corresponding (1:1) Ni(II) complexes in terms of Δlog10K values. The effect of phenanthroline substituents (4-methyl, 5-methyl, 3,4,7,8-tetramethyl, 5-nitro) on the nature of the Ni(II) complexes is evaluated.

Neocuproine Copper(II) Complexes with Bioactive Ligands in Aqueous Solution

A potentiometric titration technique has been used to determine protonation constants of neocuproine {(neo): 2,9-dimethyl-1,10-phenanthroline} and bioactive ligands {(N,O-donor chelator, N,O): glycine (gly), leucine (leu), methionine (met), phenylalanine (phe), tyrosine (tyr), tryptophan (trp), asparagines (asn), glutamine (gln), aspartic acid (asp), glutamic acid (glu)} and their binary and ternary stability constants with copper(II) ion were determined at the constant ionic strength 0.1 M KCl and at 298.15 K. The protonation constants of neo and bioactive ligands and their stability constants of the binary and ternary copper(II) complexes were computed from the potentiometric titration data using BEST program. Furthermore, SPE program was used to determine the distribution of the species formed in solution medium. The stability of the ternary copper(II) complexes are compared with those of the corresponding the stability of the binary copper(II) complexes with regard to ΔlogK values.

Determination of Stability Constants and Thermodynamic Parameters for Ciprofloxacin-HCl With Some Transition Metal Ions by Potentiometric Titration Technique

This study included calculating the stability constants and stoichiometries of some binary complexes formed from the interaction of seven of metal ions (Cr+3,Mn+2,Co+2,Ni+2,Cu+2,Zn+2 and Cd+2) with Ciprofloxacin-HCl. This study was carried out using Potentiometric Titration Technique at different concentrations of the drug and the metal ion and at temperatures (288,298,310,318 and 328 K±0.1) in aqueous solution. Although, there are many methods available to study the stability of metal-ligand complexes, pH-metric is most frequently used to determine the stability constants. Hence, (Calvin - Bjerrum pH-metric titration technique) as adopted by Irving–Rossotti was used to calculate of stability constants. The results of the concentration effect study showed that the formation of complexes were more stable in dilute solutions, and through study of the temperature effect it was concluded that the stability of the complexes can be increased with raising temperature, and the stability constants value obtained were used in the calculation of thermodynamic parameters . The results of this study also showed that the ciprofloxacin tends to form two types of metal complexes in the solution (ML1),(ML2) and this indicates that the reaction ratio between the drug and the metal ion was (1:1) and (1:2)(M:L) respectively for all metal ions. These ratios depended on the nature of the ligand or the metal ion, and the stability of the complexes formed increases according to the following arrangement (Mn+ 2< Co+ 2< Ni+ 2< Cu+ 2> Zn+ 2) and this arrangement is compatible with Irving Williams’s arrangement for the stability of the elements.

전위차적정(Potentiometric titration)기법에 의한 입자성 물질의 등전점(Point of zero charge) 파악에 대한 기초 연구

전위차적정(Potentiometric titration)기법에 의한 입자성 물질의 등전점(Point of zero charge) 파악에 대한 기초 연구

Complex Formation of Phytic Acid With Selected Monovalent and Divalent Metals.

The formation of metal complexes with phytic acid is a complex process that depends strongly on the metal-to-ligand molar ratio, pH value and consequent protonation level of the phytate ligand as well as accompanying side reactions, in particular metal hydrolysis and precipitation of the formed coordination compounds. In the present work, the potentiometric titration technique was used in combination with a detailed analysis of the equivalent point dependencies for selected biologically relevant monovalent and divalent cations from the groups of alkaline earths and transition metals, namely: Mg(II), Zn(II), Fe(II), Cu(I), and Cu(II) ions. The investigation of complex formation mechanism, the evaluation of the species formed, and the identification of other side reactions was based on the examination of three distinct equivalent points, which were detectable by alkalimetric titrations of phytic acid in the presence of selected metal ions. It has been demonstrated that alkaline earth metals interact with different binding site(s) than the transition metals, and experiments with both oxidation states of copper revealed similar complexing characteristics, which depend mainly on the ionic radius (and not on the ionic charge as initially expected). Quantitative data on phytate complexation, hydroxide formation and complex precipitation are presented herein for all metals studied, including Cu(I), which was investigated for the first time by means of alkalimetric titration.

Equilibrium, DNA Cleavage and Antimicrobial Studies of Cu(II) and Zn(II) Complexes with Novel 1-Propionyl-4-methyl-3-thiosemicarbazide

Cu(II) and Zn(II) metal complexes with novel Schiff base 1-propionyl-4-methyl-3-thiosemicarbazide (PMTSC) were synthesized and characterized by LC-MS, IR, 1H NMR (D2O exchangeable), 13C NMR and UV-visible spectra, ESR, TGA, molar conductance and magnetic susceptibility measurements. The spectro-analytical studies revealed the composition of complexes as ML2 for Cu(II)-PMTSC and Zn(II)-PMTSC complex. The proton-ligand dissociation constant and metal-ligand formation constants of PMTSC with Zn(II) have been determined in 70 % (v/v) DMF-water medium at 0.1M (KNO3) ionic strength and 303 K using potentiometric Irving-Rossotti titration technique. The results revealed that PMTSC acts as monobasic ligand by releasing proton from amide via enol form and forms 1:2 (Zn-L) complex in solution. The cleavage of plasmid pBR322 DNA without any additives was monitored by gel electrophoresis and these complexes exhibited hydrolytic cleavage of plasmid DNA. The antibacterial activity of the Schiff base and its Cu(II) and Zn(II) complexes were tested against Gram-positive and Gram-negative bacteria.

Investigation of the Specific Ion Interactions and Determining Protonation Constant of 3,5-Dihydroxy-2-(3,4,5-trihydroxybenzoyl)oxy-6-[(3,4,5-trihydroxybenzoyl)oxymethyl] oxan-4-yl] 3,4,5-trihydroxybenzoate at Different Ionic Strength

In this research, the protonation constant value of tannic acid was determined at 25 °C and different ionic strengths (0.1 to 0.7 mol/dm3 NaCl) using potentiometric titration technique. The dependence of protonation constant on ionic strength was modeled and discussed by a Debye-Huckel type equation. Then, based on the obtained data from experiments, the minimizing Sum of Squares Error (SSE) was done by Microsoft's Excel solver program and the most suitable model was chosen. After optimization, the protonation constant of tannic acid at different ionic strengths was calculated and curves of log Kcal and log Kexp were compared. Finally, Daniele constants of C and D were measured and the Specific Ion interaction Theory (SIT) was assessed for this weak acid. The obtained results show that the protonation constants of tannic acid decrease with increasing ionic strength.

Comparison of the efficiency of two imidazole-based dicationic ionic liquids as the catalysts in the synthesis of pyran derivatives and Knoevenagel condensations

In the present work, 3,3′-(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) dichloride ([C4(MIm)2]·2Cl) and 3,3′-(butane-1,4-diyl)bis(1-methyl-1H-imidazol-3-ium) hydrogen sulfate ([C4(MIm)2]·2HSO4) were prepared via adequate, solvent-free methods and characterized using FT-IR, 1H NMR, 13C NMR, and potentiometric titration techniques. These reagents were investigated in the synthesis of 5-arylidene (thio)barbituric acids, 2-arylidene malononitriles, 4H-pyrans, and pyrano[2,3-d] pyrimidineones, and their catalytic activities were compared in the promotion of these reactions. Based on the obtained results, we found that [C4(MIm)2]·2Cl showed more catalytic efficiency where a basic or weak acidic media is needed. In contrast, [C4(MIm)2]·2HSO4 is a powerful catalyst in reactions needing acidic catalysts to enhance the reaction rate. Using these reagents, the products were formed under mild and eco-friendly conditions in excellent yields during short reaction times without needing column chromatography for work-up.

Relations between chloride determination in real concrete structures by X-ray fluorescence spectroscopy and by potentiometric titration

The technique of X-ray fluorescence spectroscopy is a non-destructive method used in several applications in Civil Engineering for the qualitative and quantitative determination of chemical elements in different materials. This technique allows the analysis of materials by atomic excitations and identification of spectra obtained from defined wavelengths interpreted for each chemical element present in the material in a precise and fast quantification, optimizing characterization analysis in a laboratory. Although the benefits obtained from this technique are clear, problems regarding the quantification of chloride ion in concrete powder samples, obtained from real structures, end up, giving significant errors in relation to its quantification, which, in turn, overestimate the chloride concentration in the profiles more than 500%. In this way, this work presents a correlation between two methodologies using concrete powder samples from structures present in a marine environment for more than 40 years. These samples were analyzed by X-ray fluorescence spectroscopy and potentiometric titration techniques in order to establish a correlation between the methods. The obtained results showed that there is a relationship between both techniques with a determination coefficient close to 1.

A long-time stability study of 50 drug substances representing common drug classes of pharmaceutical use.

For assurance of the quality of active pharmaceutical ingredients (APIs) used for manufacturing medicines, the analytical requirements of the European Pharmacopoeia serve as a guideline and have a binding character. Within a particular timeframe, an API is considered to comply with predefined specifications. If applicable, it can be used for the manufacturing of a finished pharmaceutical product. The objective of the study presented here was to assess the long-term stability of 50 drug substances with an age of 20-30years or even older in some cases. The substances are part of a collection of old pharmaceuticals at the Institute for Pharmacy in Würzburg, Germany, and represent commonly used drug classes containing β-blockers, β-sympathomimetic drugs, anticholinergics, anti-infectives, non-steroidal anti-inflammatory drugs, antipsychotics, antihistaminic drugs, and one antiarrhythmic drug. The content and the degradation profile of the items were determined by means of potentiometric titration and liquid chromatography techniques based on pharmacopoeial approaches for impurity profiling covering all process and degradation related substances. The results of the study show that 44 out of 49 tested substances still complied with specifications of the current pharmacopoeias. For metipranolol, which is not monographed in any pharmacopoeia, a small degradation by hydrolysis was observed. In one lot of ampicillin sodium, atenolol, atropine, penbutolol, and salbutamol, at least one impurity did not meet the acceptance criteria, respectively. Some impurities were not related to degradation. However, a surprisingly high chemical stability of the old drug substances was revealed after more than two decades of storage.

A Novel Microfluidic Assembly of a Biodegradable Nanostructures Designed for Site Specific Delivery of Anticancer Peptide Site Specific Delivery of Anticancer Peptide

Ran is a small RAS-related GTPase and is overexpressed in breast carcinoma to induce malignant transformation and metastatic growth. A novel series of antiRan-GTPase peptide (CK-10), which inhibits Ran hydrolysis and activation, have suboptimal activity in vitro due to low bioavailability and poor delivery. To overcome these disadvantages, we delivered the CK-10 peptide by encapsulating it in PLGA-based nanoparticles (NP). The successful delivery of CK-10 can prevent Ran activation by blocking a regulator of chromosome condensation 1 (RCC1) following peptide release directly in the cytoplasm after endocytosis of the novel NP(s). A novel hydrodynamic flow technique is designed to avoid the drawbacks with a double emulsion solvent evaporation technique. Loading efficiency and in vitro release were measured by modified Lowry assay, size was characterized by dynamic light scattering, tuneable pore resistive sensing and laser obscuration time, zeta potential was measured by laser anemometry, morphology was scanned by electron microscopes and laser obscuration time. Water absorption and its associated changes in the physicochemical properties were measured by various color indicator and potentiometric titration techniques tounderstand the fundamental biodegradation process. PLGA/β-cyclodextrin nanoparticles showed the highest peptide loading (53.92%m/m) for the novel microfluidic technique with the highest cumulative release of 91.38%.