pH-metric Titration Research Articles

METHOD FOR IDENTIFYING THE EQUIVALENT FRAME OF A SOLUTION BY ANALYZING TITRATION VIDEO IMAGES USING AN AUTOMATIC APPROACH

Determination of equivalence in inorganic chemistry can be achieved by various methods, such as colorimetric titration, conductimetric titration and pH-metric titration. However, these traditional methods often require repetition to guarantee reliable results, increasing the time and cost of the experiment. In response to this limitation, some authors have suggested a semi-automatic approach based on colorimetric titration, although this also has subjective aspects. The aim of this article is to propose a new method based on intuitive observation to identify the equivalent frame in a titration video. This approach relies on the use of the KNN classifier to automate the detection of the reference frame within a predefined confidence interval. To facilitate this automation, a dataset was built up from experiments at the Groupe Chimie de lEau et Substances Naturelles (GCESNA) laboratory at the Institut National Polytechnique HouphouetBoigny (INP-HB).The performance of the KNN algorithm was effectively assessed by evaluating it against the performance indicators of precision, recall and F-measure. The results obtained are as follows: Precision: 92.2%, Recall: 91.7% and F-measure: 92.0%. These experimental results demonstrate the effectiveness of the KNN algorithm in frame classification.

Novel sight into Mn(II) complexation with some tri- and tetradentate ligands in aqueous solutions. Specific aspects of interacting with β-aminotricarballylic acid

For the first time the XRD data of β-aminotricarballylic acid (BATCA) hydrochloride crystals are obtained. The acid-base properties of BATCA are presented herein, as compared to aspartic (AA), citric (CA), iminodiacetic (IDA), and nitrilotriacetic (NTA) acids. The comprehensive analysis of composition, pH distribution areas, and stability constants of manganese(II) complexes is carried out from the pH-metric titration and NMR relaxation (0.47 T) experiments at 298 K. Equilibrium constants were obtained using the CPESSP and STALABS computer programs. The approach based on the values of the spin–spin and spin–lattice relaxivities ratio (r2/r1) is used to assess the number of water molecules bound to Mn2+ ion in its complexes in aqueous solutions. This information is useful for prediction of increasing the contrast of MRI-images by manganese(II) complexes, as well as for analyzing the diversity of the complex structures in the solutions.

Assessment of the rehabilitation programs effectiveness in patients with painful external genital endometriosis

In patients with a painful form of external genital endometriosis (EGE), the prevailing symptom is chronic pelvic pain, which significantly reduces the quality of life (QoL). It causes disorders of the physical, psycho-emotional and sexual health of women of reproductive age, leading to distress, maladaptation, anxiety-depressive disorders, disruption of social functioning and family relationships. Objective. To evaluate the effectiveness of the rehabilitation program for women with a painful form of EGE after radical treatment in the rehabilitation period. Materials and methods. In the examined cohort were included a total of 104 patients of reproductive age 42.4±3.7 years with a painful form of EGE after radical treatment: Group 1 – 49 women with "active" rehabilitation; Group 2 – 55 patients with "passive" rehabilitation tactics in accordance with standards and National Clinical Guidelines. Integral assessment of QoL (objective) was performed using clinical, laboratory (cancer antigen-125 (CA-125), cancer antigen-19.9 (CA-19.9), interleukin-6 (IL-6), tumor necrosis factor (TNF), femoflor – 16, pH-metric titration), and instrumental studies (ultrasound, magnetic resonance imaging (MRI)). At the control points: before, in 5–9 days, 1,3,6 and 12 months after surgical treatment. Results. Patients with "active" rehabilitation tactics (Group 1) had a significantly more pronounced decrease in the levels of the assessed biomarkers in blood serum, normalization of the urogenital tract microbiocenosis and restoration of pelvic organs and structures, unlike patients in the comparison group. Conclusion. The use of comprehensive personalized rehabilitation in patients with painful form of EGE after radical treatment has demonstrated its effectiveness. Widespread introduction of rehabilitation programs into routine clinical practice is necessary.

COMPLEXATION OF SILVER (I) C 2-ETHYLIMIDAZOLE

The acid-base properties of 2-ethylimidazole were studied by pH-metric titration (EM). Using the literature data and our own results, a number of changes in the acid-base properties (pКa) of imidazoles have been established: ethylimidazole (7,93)> imidazole (7.05)>2-phenylimidazole (6,48)>2-aminobenzimidazole (6,11)> benzimidazole (5,53)>2-phenylbenzimidazole (5,23)>2-mercaptoimidazole (2,97)>1-methyl-2-mercaptoimidazole (2,11). Method The process of complexation of silver(I) with 2-ethylimidazole in the temperature range of 273-318K was investigated using potentiometric titration using a silver electrode. It has been established that the increase in temperature does not affect the stoichiometric composition of complex particles formed in the Ag-EM-H2O system. The results obtained show that as the temperature increases, the stability constants decrease. On the basis of diagrams, the distribution of complex particles depending on the ligand concentration is shown that in System Ag-EM-H2O is mainly dominated by the bis-substituted complex, the yield of which at EM concentrations above 1·10-2 mol/l is 100%. The thermodynamic functions of the formation of 2-ethylimidazole silver complexes have been calculated. It has been established that complexation reactions are exothermic. Spontaneous occurrence of complexation reactions in the system Ag-EM-H2O contributes to a negative change in enthalpy.

Dissociation constants of relevant secondary organic aerosol components in the atmosphere

The presented studies focus on measuring the determination of the acidity constant (pKa) of relevant secondary organic aerosol components. For our research, we selected important oxidation products (mainly carboxylic acids) of the most abundant terpene compounds, such as α-pinene, β-pinene, β-caryophyllene, and δ-3-carene. The research covered the synthesis and determination of the acidity constant of selected compounds. We used three methods to measure the acidity constant, i.e., 1H NMR titration, pH-metric titration, Bates-Schwarzenbach spectrophotometric method. Moreover, the pKa values were calculated with Marvin 21.17.0 software to compare the experimentally derived values with those calculated from the chemical structure. pKa values measured with 1H NMR titration ranged from 3.51 ± 0.01 for terebic acid to 5.18 ± 0.06 for β-norcaryophyllonic acid. Moreover, the data determined by the 1H NMR method revealed a good correlation with the data obtained with the commonly used potentiometric and UV-spectroscopic methods (R2 = 0.92). In contrast, the comparison with in silico results exhibits a relatively low correlation (R2Marvin = 0.66). We found that most of the values calculated with the Marvin Program are lower than experimental values obtained with pH-metric titration with an average difference of 0.44 pKa units. For di- and tricarboxylic acids, we obtained two and three pKa values, respectively. A good correlation with the literature values was observed, for example, Howell and Fisher (1958) used pH-metric titration and measured pKa1 and pKa2 to be 4.48 and 5.48, while our results are 4.24 ± 0.10 and 5.40 ± 0.02, respectively.

КИСЛОТНО-ОСНОВНЫЕ РАВНОВЕСИЯ ПЕКТИНА И ХИТОЗАНА В ВОДНЫХ РАСТВОРАХ

Using the pH-metric titration method, the degree of deacylation of chitosan was determined to be 100 % and the degree of acylation of pectin was 20 % and their characteristic dissociation constants were 5.94 and 5.10, respectively. It has been shown that the solubility threshold of chitosan CS5 corresponds to the degree of ionization of amino groups equal to 22 %. It has been established that the dissociation constant of chitosan increases with increasing degree of dissociation, while for pectin it does not depend on the degree of dissociation.

COMPOSITION AND THE RELATIVE STABILITY OF SULFUR DIOXIDE INTERACTION PRODUCTS WITH POTASSIUM AND MONOETHANOLAMMONIUM TAURATES AQUEOUS SOLUTIONS. PROLONGED-ACTION CHEMOSORBENT

Much research attention has been paid to amino acids as an alternative to amino alcohols for capture of sulfur dioxide. Taurine (Tau) occupies a special place among amino acids. This study was stimulated by the limited literature data on the nature of the interaction of SO2 with Tau salts aqueous solutions, the composition and relative stability of the corresponding reaction products. Chrono-pH-, chrono-redox- and chrono-conductometric studies of SO2 chemisorption with potassium taurate (TauK) and monoethanolammonium (TauMEA) aqueous 0.1 M solutions were carried out in the temperature range 293–313 K to study these processes. The maxima on the differential pH-metric titration curves positions coincide with the positions of the jumps on the integral and maxima on the redox-metric titration differential curves, as well as with breaks on the conductometric curves position. Δk negative values indicate the formation of weakly dissociated particles or less mobile ions in the solutions under study that is confirmed by the data of mathematical calculations. Using a mathematical model that takes into account the law of mass action, material balance and electrical neutrality principle, SO2 – TauK – H2O solutions ion-molecular composition and ionic strength were calculated. With an increase in the chemisotption SO2 amount, the taurate anions concentration decreases due to the hydrolytic transformation into zwitter ions +NH3CH2CH2SO2O - and the sequential transformation of hydrotaurate-sulfite (4:1 and 2:1; I and II), taurate-sulfite (2:1; III), hydrotaurate-hydrosulfite (2:1; IV) and taurate-hydrosulfite (1:1; V) associates. The concentration and thermodynamic constants for the formation ionic associates I–V were calculated. TauK input into impregnated fibrous chemisorbents (IFCS) composition obtained by impregnating viscose fibers with monoethanolamine aqueous 0.25 M solutions (IFCS-0.25MEA) leads to a synergistic increase in quantity of adsorbed SO2. IFCS-0.25MEA-TauK are long-acting sulfur dioxide chemisorbents, and TauK itself serves as a promoter-modifier towards IFCS-0.25MEA preventing the MEA removal from IFCS surface by the GPS flow due to the ionic associates formation and promoting deeper HOCH2CH2NH2 «response».

Divalent transition metal complexes of nitrogen, oxygen and sulfur containing ligand: design, structural, spectral, pH-metric, theoretical molecular modeling, analytical and mechanism studies

In the present study, the 1-Nicotinoyl-4-phenyl thiosemicarbazide (H2NPT) multidentate nitrogen, oxygen and sulfur containing ligand is being synthesized in a simple single step reaction by condensing 1:1 molar ratio of ethanolic solutions of both phenyl isothiocyanate and nicotinoyl hydrazine. The prepared H2NPT and its complexes with Co2+, Ni2+ and Zn2+ and Cu2+ were characterized by pH-metric titrations, elemental analysis, FTIR, electronic spectra and thermogravimetric (TGA) analyses. The association constant of the ligand and the stability constants of its complexes were calculated by pH-metric measurements in 50% ethanol–water mixture. Also, DFT method was used to draw the geometry of all compounds and the parameters such as bond lengths, bond angles, dipole moment, Frontier orbitals (HOMO, LUMO), MEP and other energetic parameters (optical energy gap, softness, hardness, electronegativity) were evaluated. The prepared H2NPT reacted with Co2+, Ni2+ and Zn2+ and Cu2+ metal ions to form colored precipitates that were readily floated to the surface solution using oleic acid (HOL) surfactant with vigorous shaking of the flotation cell. The heavy metals' concentrations in the dissolved precipitates are determined by flame atomic absorption spectrometry (FAAS). The different parameters affecting the flotation process were thoroughly investigated, viz. pH of sample solution, concentration of ligand, metal ions and HOL, temperature and interfering ions. Nano-gram quantities of Cu2+, Co2+, Ni2+ and Zn2+in 1500-ml samples are quantitatively determined with 1-Nicotinoyl-4-phenyl thiosemicarbazide (H2NPT) at pH 3.0–6.5 for Cu2+ and at 7.0–7.5 for Co2+, Ni2+ and Zn2+. The concentrations of these heavy metals are increased 300-fold. Interferences, on the flotation process, from various foreign ions were avoided by adding excess H2NPT. The mode of chelation between H2NPT and the investigated metal ions is proposed to be through the S, N and/or O atoms of the ligand. The mechanism of flotation is proposed to be due to an electrostatic interaction between the HOL surfactant and the formed metal–ligand complexes through H-bond formation. The proposed multi-element flotation methodology has been utilized for the determination of the analytes in certified reference materials, alloys, synthetic mixtures and in water samples with a recovery % more than 90% and a relative standard deviation (RSD), as a precision < 2%.

A new route of production of the meso-porous chitosan with well-organized honeycomb surface microstructure from shrimp waste without destroying the original structure of native shells: Extraction, modification and characterization study

The highly active bio-polysaccharide based compound namely chitin and chitosan have been extracted from shrimp shell which usually expelled out extensively from food processing industries and considered as waste materials. However, by conducting demineralization, de-proteinization and deacetylation on it which could be a new route of production of valuable meso-porous chitosan that possesses a noteworthy well-organized honeycomb like surface microstructure which undoubtedly capable to form sustainable bio-composites. Whereas the honeycomb like microstructures showed a well-defined pore canals (Pc) and pore canal tubes (Pct) onto their surface. The samples were characterized via ATR-FTIR spectroscopy, High resolution SEM, AFM, EDX, XRD and 13C solid-state Cross-Polarization Magic Angle Spinning (CPMAS) NMR. The molecular weight(M‾v) of isolated chitin and chitosan were determined by viscosity and the values were 1.06 × 106(DPv = 5228), 1.8 × 104(DPv = 116) respectively besides degree of deacetylation (DDA) were measured by ATR-FTIR spectroscopy, CPMAS NMR, pH-metric titration and the values were 24&21 for chitin and 84&82 for chitosan. The results suggest that the shrimp shell waste is an attractive source of well-organized honeycomb like meso-porous chitin and chitosan with regular surface microstructures which might have a significant/potential application into the sustainable bio-composite formulation due to various industrial and biomedical sector indeed.

PH-metric titration technique for the study of metal-complexes of substituted 2- Oxo-2H-Chromene-3-Carbohydrazide derivatives in solution: calculation of stability constants

Background: In coordination chemistry, the stability of complexes is expressed in terms of the formation constant of complexes. In coordination complexes, the temperature is very important. It plays an important role in complex formation reaction. Temperature affects metal-ligand stability constant (log K) and proton-ligand stability constant (pK). The metal ion Mn2+, Co2+, Ni2+, and Cu2+ at different temperatures form complexes with 4-sulfamethoxazoleazo-3-methyl-2-pyrazolin-5-one are reported. The metal-ligand stability constant (logK) and proton-ligand stability constant (pK) of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) with organic ligand n-[2-hydroxy-1-napthalydene]-2-methylanilline at 0.1 M ionic strength in 60% dioxane-water medium is studied. The study of thermodynamic parameters and stability constant of complexes of substituted thiazole Schiff bases with rare earth metal ions in mixed solvent is reported. Objective: The study of coordination compounds and a lot of work has been done on metal-ligand stability constant. The same transition metal ion form complexes with substituted pyrazole for this metal-ligand stability constant are determined. Method: Pointwise Calculation Method Half Integral Method. Result: The values of logK1 and logK2 are determined from the metal-ligand formation curve at formation numbers 0.5 and 1.5. In all cases, logK1 is greater than logK2. The ratio logK1/logK2 is positive and greater than one in all systems. This implies that there is little or no steric hindrance to the addition of the secondary ligand molecules. The difference between logK1 - logK2 is usually positive. If the difference between logK1 and logK2 is less than 2.5, simultaneous formation of 1:1 and 1:2 complexes occurs and if it is more than 2.5, then stepwise complex formation occurs. In the present case, in all systems, it is less than 2.5. This indicates the simultaneous formation of 1:1 and 1:2 complexes takes place. Conclusion: A pH-metric study of Substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), and Mn(II) occurs. The graphical representation of the curve shows that the acid + ligand curve is separated from the corresponding acid + ligand + metal curve in this system. The formation of a complex is indicated. Half integral method and pointwise calculation method give nearly similar results. The values of stability constants for all systems indicate that the complexes formed in these processes are stable.

Preparation, investigation, DFT, pH-metric and cyclic voltammetry of Cr(III), Fe(III), Co(II), Ni(II) and Cu(II) complexes derived from 2-(2-((2Z,3Z)-3-(hydroxyimino) butan-2-ylidene) hydrazineyl)-2-oxo-N-(pyridin-2-yl) acetamide (H3BYPA) and evaluation of their biological activity

Binuclear Cu(II), Co(II) and Ni(II) and mononuclear Fe(III) and Cr(III) complexes derived from new ligand, namely 2-(2-((2Z,3Z)-3-(hydroxyimino) butan-2-ylidene) hydrazineyl)-2-oxo-N-(pyridin-2-yl) acetamide (H3BYPA) have been prepared and identified by elemental analysis, magnetic measurements and spectral methods. The separated complexes appointed the general formula, [M2(HBYPA)(H2O)mCln].xH2O where M = Co(II) and Cu(II) and x = 0 and 3, respectively. IR data detected that the ligand behaves as monobasic NO bidentate in [Fe(H2BYPA)2Cl(H2O)].H2O complex. However, as dibasic tetradentate in [Cr(HBYPA)Cl(H2O)], [Co2(HBYPA)Cl2(H2O)2] and [Cu2(HBYPA)Cl2(H2O)2].3H2O complexes. Furthermore, H3BYPA behaves as tribasic pentadentate in the binuclear [Ni2(BYPA)Cl(H2O)4].4H2O complex,. pH-metric titration was accomplished in 50% water-dioxane mixture at 298, 318 and 328 K, respectively and the ligand's dissociation constant as well as the complexes’ stability constants were recorded. Also, the thermodynamic and kinetic parameters for the several thermal degradation phases of the complexes were calculated using the Horowitz–Metzger and Coats–Redfern approaches. The optical band gap values were compared to those produced by DFT and found to be equivalent. Moreover, antitumor and antibacterial activities of the compounds have been tested. Finally, the ligand and complexes docking study was utilized against HEPG-2 and MCF-7 by Schrödinger suite program using XP glide protocol.

Activated eco-waste of Posidonia oceanica rhizome as a potential adsorbent of methylene blue from saline water

A new activated adsorbent was produced from the debris of Posidonia oceanica rhizomes (POR). POR were activated in acetic acid and utilized as an eco-adsorbent for the removal of cationic dye methylene blue (MB) from saline solutions. The purified Posidonia oceanica rhizomes (PPOR) and its activated form (APOR) were characterized by elemental analysis, pH-metric titration, Fourier transformer infrared (FTIR), and surface area measurements, which inferred a remarkable activation of APOR. An enhancement in the free acidic sites was confirmed. The adsorption data obtained were analyzed using Langmuir, Freundlich, Temkin, Dubinin-Kaganer-Raduskavich (DKR), and Redlich and Peterson (RP) isotherm models. The obtained data from these isotherm models were tested using some error functions (residual root mean squares error (RMSE), sum square error (SSE), and chi-square test (X2) function). Temkin isotherm model was the best isotherm fits the experimental data of APOR. Kinetic data were evaluated by pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion models. The adsorption rate was found to follow PSO model with a good correlation (R2 = 0.999–1). A suggested, endothermic, multilayer, combined electrostatic and physical adsorption mechanism may be responsible for the removal of MB from water utilizing APOR. Adsorption is anticipated to start with chemisorption on active functional groups of adsorbent’s surface followed by physisorption of the subsequent layers through adsorbate–adsorbate interaction. The removal process was successfully applied for MB-spiked saline and brackish water with removal efficiencies of 51.7–97.2%. The results revealed that activated Posidonia oceanica rhizomes is a promising adsorbent for the removal of the methylene blue dye from real saline and brackish water with high removal efficiencies.Graphical

Facile synthesis and characterization of folic acid-modified silica nanoparticles and its exploration for adsorptive removal of aluminum(III) from aqueous media

In the current study, folic acid-modified silica nanoparticles (FA-SNPs) were fabricated and used for the removal of Al(III) from aqueous media via solid-phase extraction (SPE) procedure before its spectrometric determination using flame atomic absorption spectrometry (FAAS). The prepared adsorbent was characterized by elemental analysis, infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area measurement, and pH at a point of zero charge (pHpzc). Thermogravimetric analysis (TGA) was used to prove the thermal stability of the prepared adsorbent. The influence of several parameters including initial pH, amount of adsorbent, time of contact, initial adsorbate concentration, and the effect of foreign ions was studied. The outcomes presented that optimum adsorption of Al(III) was achieved at pH 3.5, contact time of 30 min, adsorbent dosage of 25 mg, and 25 °C. The experimental data agreed well with the pseudo-2nd order model and was fitted by the Langmuir model with adsorption capacity equal to 17.52 ± 0.122 mg/g. Thermodynamic analysis revealed that the adsorption of Al(III) was spontaneous and exothermic. The procedure was successfully applied for the recovery of Al(III) spiked to some real water samples. The regeneration study using HNO3 indicated the excellent regenerative power of the prepared adsorbent. Moreover, pH-metric titration was used to prove the complexation between Al(III) and the surface of the prepared adsorbent. The obtained results showed that FA-SNPs is an effective, eco-friendly, and low-cost adsorbent that can be used for the removal of Al(III) from aqueous solution.

Determination of Stability Constant of The Complexes of Metal Ion Fe(III), Mn(II) And Cr(III) With Some Substituted 2-Oxo-2H-Chromene-3-Carbohydrazide Derivatives at 0.1 M Ionic Strength at 42oC

Proton ligand and metal ligand stability constant are measured for Fe(III) and 1, 2-dihydroxy benzene and 1, 5-disulphonic acid complexes . Determination of stability constant of substituted of pyrazoles with rare earth metals form complexes are reported . Effect of temperature on formation constants of 2 acetylpyridine(N benzoyl)glycine hydrazone with lanthanide(III) ions at different ionic strengths are reported. Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Bjerrum-Calvin titration technique . Kabadi , Jahagirdar and Narwade have determined pK values of salicylaldehyde, salicylic acid and sulphonic acid respectively by similar procedure. The metal ligand stability constant of some β-diketones are reported . Stability constants have investigated for some substituted pyrazolines, isoxalline and diketone . The method most frequently applied for study of complex equilibria is pH-metric titration technique . Stepwise formation of mononuclear binary complexes is described by set of equilibrium constants. For pH-metric measurements an electrode must be selected. According to Bjerrum, Martell and Calvin , the formation of complex MLN is stepwise process and one has to deal with a series of equilibria of the type: Irving and Rossotti, Herson and Gilbert , Wilkins and Lewis and Rossotti and Rossotti have determined stability constant by Calvin-Bjerrum titration technique . The value of nA,n, pK, log K1 and log K2 are evaluated by Irving and Rossotti's equation. The stability constant and thermodynamic parameters of complexes containing lighter lanthanides , copper(II) , calcium and magnesium are reported. It is also important in environmental studies , medicinal and industrial chemistry . Effects of transition metal on stability constant of complexes have studied by pH metric method . Bendi , Janrao and Ramteke have studied stability constant of ligands with lanthanide metals complexes.The present work involves pH metric study of substituted 2-oxo-2H-chromene-3-carbohydrazide derivatives with metal ions Fe(III), Mn(II), Cr(III) and Ti(III) at temperature42oC. The Bjerrum-Calvin titration technique as modified by Irving and Rossotti has been employed in the present study. The following three sets of titrations are carried out in sequence.

SPECTROSCOPIC STUDIES OF Cu (II) AND Co (II) COMPLEXES WITH RUTIN IN SOLUTIONS

Complexation in M (II) – Rut systems (M(II) = Co, Cu) was studied by electron absorption spectroscopy and pH-metric titration in water-ethanol solutions depending on the metal: ligand ratio (1: 1; 2: 1) and the pH of the medium. It was shown that the structure and stoichiometric composition of the complexation reaction products are influenced by such basic parameters as L:M and the pH value of the medium. Depending on the pH value, chelation involves certain binding sites, which primarily is associated with the redistribution of the electron density in the flavonoid molecule. In a weakly acidic or neutral medium, regardless of the M(II): Rut ratio, the formation of monoligand complexes of rutin with 3-d metals occurs with the participation of 5-OH and 4-C=O fragments of the A and C rings, and in an alkaline medium, chelation proceeds on the catecholic fragment of ring B rutin. Biligand complexes are formed with the participation of the gydroxo groups of the catechol fragment of each rutin molecule, and the formation of compounds with a ratio of 2:1 occurs both due to 5-OH and 4C=O and due to 3 ', 4'-OH groups. The calculated values of the stability constants of the complexes showed that the stability of the Co (II) complexes is several orders of magnitude lower than the stability of the corresponding Cu (II) complexes.

New Aspects of Complex Formation in the Gadolinium(III)–Citric Acid System in Aqueous Solution

ABSTRACT The complexation of gadolinium(III) with citric acid in aqueous solutions was studied by pH-metric titration, proton magnetic relaxation, and mathematic simulation in the pH range 2.0–10 at [Gd3+]: [H4Cit] = 1:1, 1:2, 1:3 ([Gd3+] = 1.3, 2.6, 5.0, 10.0, and 20.0 mmol L−1). In the process of simulation, the equilibrium composition, a model obtained from previously known works and including mono- and bis-citrate complexes of gadolinium(III) was taken as a basis. In this work, it is shown that a satisfactory description of the experimental data set of two independent physico-chemical methods is achieved only with the additional inclusion of citrate complexes of gadolinium(III) with higher degree of protonation and some new polynuclear complexes. The complex [GdH4Cit]3+ with the molecular form of the citrate ligand, and the polynuclear complexes [Gd2(HCit)2]°, [Gd2Cit2]2-, [Gd6(OH)2Cit6]8-, [Gd6(OH)3Cit6]9- were first detected at the molar ratio of 1:1. At two- and three-fold excess of citric acid, mononuclear bis- and tris-citrate complexes with different degrees of protonation were found, and binuclear tetrakis- and hexakis-citrate complexes [Gd2(HCit)Cit3]9-and [Gd2(HCit)4Cit2]14- at the pH > 7.5. On the example of this manuscript, the importance of applying the NMR relaxation method for identifying polynuclear complexation in systems containing paramagnetic ions is shown.

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.

Исследование комплексообразующих свойств монопроизводных янтарной кислоты с ионами меди (II) и никеля (II).

Mono-derivatives of alkenyl succinic acid are considered in this paper, also their complexes with copper and nickel ions, which structure was studied by IR spectrometry method. Protonization constants and stability constants of complexes of mono-derivatives of succinic acid with copper and nickel ions are calculated by pH-metric titration method. It has been established, that mono-derivatives of succinic acid formed more stable complexes with the copper ion.

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.

Chemical and Phase Equilibria in the Reaction between NO and O2 in the Presence of Water and CO2 at 298.15 K up to 3 MPa

New experimental data for cosolubility of carbon dioxide, nitric oxide, and nitrogen dioxide produced from the reaction in situ between nitric oxide and dioxygen in pure water at 298.15 K and up to 3 MPa are presented in this work. These data are essential to develop and validate thermodynamic models for CO2 and other gases capture and storage processes. In this work, measurements of carbon and nitrogen oxide solubilities in water are achieved; the liquid phase composition at the thermodynamic equilibrium was determined by analytical methods (ion chromatography), pH-metric titration, and a static synthetic method, and the gaseous phase composition was determined by two infrared spectrometers. The experimental apparatus and the analytical procedure were validated by studying the CO2 + water systems and comparing the experimental measurements with the literature data. On the other hand, the measurements of NO2 + water systems are original and do not exist in the literature. In order to study the behavior of the nitrogen dioxide in water, a suitable reaction mechanism was carefully chosen to predict the composition of the different nitrogen species (NO, NO2, N2O3, N2O4, HNO2, H+, NO2–, HNO3, and NO3–.) in the aqueous medium at 298.15 K. Then, a Henry constant for the studied nitric oxide systems was calculated. Some difficulties have been encountered in the stabilization of the nitrogen dioxide partial pressure due to its metastable conditions; therefore, data related to the Henry constant of this compound will not be reported.