Stepwise Stability Constants Research Articles

Dynamic Coordination between a Triphenylamine-Functionalized Salicylaldehyde Schiff Base and a Copper(II) Ion.

The coordination between a ligand and a metal is a spontaneous and uncontrollable process. In this Article, we successfully observe the formation of metal coordination in a triphenylamine-functionalized salicylaldehyde Schiff base with a copper(II) ion. The ligand TPA-Py first reacts with Cu2+ in a stepwise process to afford the dynamic complex TPA-Py@Cu2+ ([ligand]:[Cu2+] = 1:1), which further reacts with an extra copper(II) ion to afford 2TPA-Py@4Cu2+ with the following stepwise (or cumulative) stability constants: K1 = 4.0694 × 103 and K2 = 1.0761 × 106, respectively. The entire metal coordination process can be visualized, and the coordination mode of the probe toward copper was further evaluated by ultraviolet-visible/fluorescence spectra, single-crystal X-ray diffraction, density functional theory calculations, high-resolution mass spectra, and nuclear magnetic resonance spectroscopic titrations. Compound TPA-Py exhibited excellent sensitivity and specificity toward copper(II) ions in THF/water media with a low limit of detection of 2.687 × 10-7 mol L-1. In addition, TPI-An-Py can be applied to the detection of Cu2+ in real samples with satisfactory recoveries in the range of 100-112% in lake water and 98-101% in tap water. This Article not only reports an excellent fluorescence probe for copper(II) ion detection but also presents an instance for more fully understanding the metal coordination process.

Characterization of Thorium-Pyrazinoic acid complexation and its decorporation efficacy in human cells and blood

Thorium (Th) exposure to the human beings is a radiochemical hazard and the chelation therapy by suitable drugs is the major prevention approach to deal with. The present studies aimed at usage of pyrazinoic acid (PCA), which is a prodrug to treat tuberculosis, for its usage as decorporating agent for thorium from human body. The present studies provide a comprehensive knowledge on the chemical interaction and biological efficacy of pyrazinoic acid (PCA) for decorporation of Thorium from the human body. The thermodynamic parameters for Th-PCA speciation are determined by both experiment and theory. The potentiometric data analysis and Electro-Spray Ionization Mass Spectrometry (ESI-MS) studies revealed the formation of MLi (i = 1–4) species with the decrease in stepwise stability constants. All the species formations are endothermic reactions and are predominantly entropy-driven. Biological experiments using human erythrocytes, whole blood and normal human lung cells showed cytocompatibility and decorporation ability of PCA for Thorium. Density functional calculations have been carried out to get insights on interaction process at molecular level. The experimental results and theoretical predictions found to be in line with each other. Present findings on complexation of Th by PCA and its evaluation in human cells and blood would further motivate determination of its safety levels and decorporation efficacy in animal models.

Synthesis, Identification of Co(II), Cu(II) and Ni(II) Complexes with A Schiff Base–Azo Ligand Derived from Imidazol Derivatives, 4- Aminoacetophenon and 4- Chloroaniline and Study Their Physical Properties and Their Thermodynamic Stabilities

The complexes of Co(II), Cu(II) and Ni(II) were synthesized by using schiff base – azo as a ligand, which were prepared under this study by the reaction between the Schiff base diazonium salt and the imidazole derevitive. They were characterized by element analysis, FTIR spectroscopy and UV.VIS. spectroscopy. Their electric conductivity and magnetic features were determined. Their stepwise and overall stability constants and their thermodynamic data ( , and ) were determined. The results showed that all the complexes have paramagnetic features and all of them have good conductivity. The formula of the complexes under this paper were suggested by using the mole ratio method which lead to the formation of (1 : 2) metal : ligand formula for all the complexes. In all the complexes the coordinated sites was through N atoms of the azo groups and N atom of the imidazol ring. The suggested geometrical shapes of the complexes was the octahedral shape due to the ( d2sp3 ) hybridization. Their stepwise stability constants were determined, it was found that for all the complexes they were increased toward the addition of ligand that because of the chelate effect. Their overall stability constants were determined, it was found that for all the complexes were high that because of the chelate effect. Their thermodynamic functions ( , and ) were had negative value, that refer to good stability for the complexes and these results were satisfied with the spontaneous reaction and high stability complexes.

A detailed spectrophotometric investigation of the stability constants of [PdCln(OH)4-n]2− and [PdBrn(OH)4-n]2− (n = 0–4)

Complex formation of mixed palladium (II) chloro-hydroxo and palladium(II) bromo-hydroxo complexes have been investigated employing spectrophotometry at 25 °C and an ionic strength of 1.0 M. Hyperquad Simulation and Speciation (HySS) was employed to determine the ideal titration conditions and an autotitrator (equipped with a flow-through cell) was used to accurately vary the pH over 80 and 90 intervals respectively. The stability constants (log βn) for the mixed chloro-hydroxo complexes [PdCl4-n(OH)n]2− (n = 0–4), are: log β1 = 18.36, log β2 = 23.21, log β3 = 26.91 and log β4 = 29.68. These newly obtained values represent a more accurate representation for the stability constants of the mixed palladium(II) chloro-hydroxo speciation. The same experimental procedure was employed to calculate, for the first time, the stepwise stability constants of the palladium(II) bromo-hydroxo system, [PdBr4-n(OH)n]2− (n = 0–4), i.e. log β1 = 18.73, log β2 = 22.25, log β3 = 25.58 and log β4 = 28.47. Molar absorption spectra for all the complexes in question have been obtained. For both systems, complete Pourbaix diagrams were constructed from the new speciation data showing the predominant species for each system.

Structures, hydrolysis, stabilities of palladium(II) complexes containing biologically active ligands and species distribution in aqueous solution

[PdACl2](n-1)H2O complexes {A: 1,10-phenanthroline (phen), 4-methyl-phenanthroline (4-mphen), 5-methyl-1,10-phenanthroline (5-mphen), 4,7-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen)} were synthesized and characterized by CHN elemental analysis, ATR-FT-MIR and ATR-FT-FIR, 1H NMR and 13C NMR spectral measurements. n is the number of crystal water molecules in the complexes. The n value for the complexes [Pd(phen)Cl2], [Pd(4-mphen)Cl2] and [Pd(5-mphen)Cl2] is 1; for the complex [Pd(tmphen)Cl2]H2O is 2; for the complex [Pd(dmphen)Cl2]2H2O is 3. [PdACl2](n-1)H2O complexes were converted into aqua complexes derived from 1,10-phenanthroline, [PdA(H2O)2]2+, and investigated [PdAB]+ mixed ligand complexes formed between [PdA(H2O)2]2+ complexes and amino acids {B: glycine (gly) and tyrosine (tyr)}. Protonation constants of the gly and tyr, the acid dissociation constants of the coordinated water molecules in [PdA(H2O)2]2+ complexes and the stepwise stability constant of the [PdAB]+ mixed ligand complexes were determined in aqueous 0.1 M KNO3 ionic media at 298.15 K by potentiometric methods. The protonation constants of ligands, the acid dissociation constants of aqua complexes and the stepwise stability constants of mixed ligand complexes were calculated from the potentiometric data using the “BEST” software package. The concentration distribution of the various species formed in aqueous solution was obtained using the “SPE” software package under the experimental conditions described. The order of stepwise stability of the mixed ligand complexes in terms of the gly and tyr was [Pd(tmphen)(gly/tyr)]+ > [Pd(dmphen)(gly/tyr)]+ > [Pd(4-mphen)(gly/tyr)]+ > [Pd(phen) (gly/tyr)]+ > [Pd(5-mphen)(gly/tyr)]+. This study could contribute to a better understanding of the behavior of the palladium(II) complexes in biological systems.

Synthesis of Some Novel Chalcone containing Pyrazole Moiety

Compounds having the sulphonamide group has long been used as drugs for various diseases. The biological activity of these drugs is enhanced by complexation with metal ions. Transition metal Fe (II) complex of ligand derived from sulfamethizole and substituted p-cresol have been prepared and evaluated for antimicrobial activity. The products have been characterized by elemental analysis, IR, NMR, UV-Vis spectral studies, conductivity measurements, magnetic susceptibility measurements, molecular weight determination and stepwise stability constants by PH metric method. The elemental analysis revealed that the azo dye ligand coordinated to the metal ions in 1: 2 (metal-ligand) molar ratios. The complex are non-electrolytes as confirmed by their conductivity measurements. The infrared data indicates that the ligand are coordinated with meal ions through diazo (−N=N-) nitrogen and phenolic (−OH) oxygen. The spectral data suggest distorted octahedral geometry as shown in the proposed structure.

Phytate–molybdate(vi) interactions in NaCl(aq)at different ionic strengths: unusual behaviour of the protonated species

Stepwise stability constants of phytate/molybdate(vi) complexes regularly increase with the number of protons in the species, affecting their speciation and sequestration.

Complexation of mercury(II) with 1-Phenyl-2,3-dimethylpyrazoline-5-thione in 0.1 mol/L HNO3 at 273–338 K

The complexation of mercury(II) with 1-phenyl-2,3-dimethylpyrazoline-5-thione is studied by means of potentiometry in 0.1 mol/L HNO3 at 273–338 K. The composition of the complexes is determined and their stepwise stability constants are calculated. A pattern is found in altering the stepwise stability constants as the temperature and number of attached 1-phenyl-2,3-dimethylpyrazoline-5-thione molecules rise.

Interactions of bis(2,4,4-trimethylpentyl)dithiophosphinate with Nd(III) and Cm(III) in a homogeneous medium: a comparative study of thermodynamics and coordination modes.

Complexation of Nd(III) and Cm(III) with purified Cyanex301 (ammonium bis(2,4,4-trimethylpentyl)dithiophosphinate, denoted as HL) was studied in 1 % v/v water/ethanol under identical conditions by spectrophotometry and microcalorimetry. For Nd(III) , three successive complexes, NdL(2+) , NdL2 (+) , and NdL3 , formed in the solution. In contrast, four complexes, CmL(2+) , CmL2 (+) , CmL3 , and CmL4 (-) formed during the titration with Cm. Fluorescence lifetime measurements provided additional insight into the complexation of Cm(III) with Cyanex301. The stepwise stability constants for the CmLj ((3-j)+) (j=1-3) complexes are about one order of magnitude higher than the corresponding NdLj ((3-j)+) complexes. The enthalpies of complexation are endothermic for both Nd(III) and Cm(III) , suggesting that the energy required for desolvation exceeds the energy gained from the cation/ligand combination. Specifically, the enthalpy of complexation for CmL(2+) is 3.5 kJ mol(-1) less endothermic than that of NdL(2+) , implying stronger covalent interaction in CmL(2+) than NdL(2+) . However, the enthalpies of complexation for CmL2 (+) and NdL2 (+) are nearly identical, and the enthalpy of complexation for CmL3 (aq) becomes more endothermic than that for NdL3 (aq). The observations suggest that, in the ethanol/water media, the overall energetics of the Cm(III) /Nd(III) complexation with Cyanex301 could depend on a number of factors, including the extent of covalency, the degree of desolvation, and the coordination modes.

An experimental study of hydroxo complex formation in basic and near-neutral solutions of rare-earth elements and yttrium at 25 ºC

We have studied the hydrolytic behavior of Y3+ and trivalent ions of rare earth elements in aqueous solutions at 25ºC. The stepwise stability constants of hydroxide complexes were measured by spectrophotometry, using m-cresol purple and 1-(2-pyridylazo)-2-naphthol as pH indicators at an ionic strength no more than 0.0005. The results showed that at pH ranging between 6.0 and 11.0 in freshly prepared solutions of REE trichlorides, lanthanides are presented as Ln3+, Ln(OH)2+, Ln(OH)2, and Ln(OH)3. The plots of the formation constants of +0 monohydroxo complexes of 4f n ions M3+ versus atomic number Z deviate from smooth ones and consist of four convex curves. This phenomenon is also observed in normalized spectra of REE concentrations in natural objects and is known as the tetrad effect. The obtained data give an insight into the relationship between REE complex formation and REE fractionation in geochemical processes and can be used for physicochemical modeling of geochemical systems.

Complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions. Crystal structure of the uranyl complexes {[UO2(bipy)(cpc)]2O2} and [UO2(cpc)2(H2O)2] (bipy = 2,2′-Bipyridine, cpc− = cyclopropanecarboxylate anion)

The complexation of hexavalent U, Np, and Pu with cyclopropanecarboxylate anions, cpc−, in aqueous solutions was studied. The stepwise concentration stability constants of the complexes PuO2(cpc)i2−i (i = 1, 2, 3) are as follows: logK1,2,3 = 2.63 ± 0.20, 1.61 ± 0.20, 1.43 ± 0.20, respectively; the overall concentration stability constant of the complex PuO2(cpc)3− is logβ3 = 5.67 ± 0.60. The complexing properties of the cpc− anion are very close to those of butyrate and isobutyrate anions. Two crystalline uranyl compounds were synthesized: {[UO2(bipy)(cpc)]2O2} (bipy = 2,2′-bipyridine) and [UO2(cpc)2(H2O)2]. The specific feature of the first complex is that it contains peroxide ion. Its appearance may be due to the formation of the cationic moiety via hydrolytic uranyl dimer. The second compound forms a 3D structure, with the complexes linked via hydrogen bonds.

Synthesis, spectral characterization, molecular modeling and in vitro antibacterial activity of complexes designed from O2, NO and NO donor Schiff-base ligand

A new chelating agent, N′-(4-methoxybenzylidene)-2-oxo-2-(phenylamino)acetohydrazide (H2OMPH) and its complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and U(IV)O22+ ions have been prepared and characterized by conventional techniques. The spectral data indicated that the ligand coordinates as neutral bidentate with Cu(II), Mn(II), U(IV)O22+ and Hg(II), neutral tridentate with Ni(II), mononegative tridentate with Co(II) and binegative tetradentate with Zn(II) ions. On basis of magnetic and electronic spectral data an octahedral geometry for Mn(II), Co(II) and Ni(II) complexes and a square planar geometry for Cu(II) complex have been proposed and confirmed by applying geometry optimization and conformational analysis. The protonation constants of H2OMPH and the stepwise stability constants of its complexes are calculated at 298, 308 and 318k as well as their thermodynamic parameters. Also, the Kinetic parameters (Ea, A, ΔH*, ΔS* and ΔG*) were determined for each thermal degradation stage of some complexes using Coats–Redfern and Horowitz–Metzger methods. Moreover, the ligand and some complexes were screened for in vitro antibacterial activity against Staphylococcus epidermalies (St. epid); Streptococcus pyagenies (Strp. py.) as Gram +ve bacteria and Escherichia coli (E. coli); Klebsiella spp. (kleb. spp.) as Gram −ve bacteria using inhibition zone diameter.

Rhenium(V) complexation with 4-methyl-1,2,4-triazolethiol-5 in 7 M hydrobromic acid

The complexation of rhenium(V) with 4-methyl-1,2,4-triazolethiol-5 in 7 M hydrobromic acid was potentiometrically studied. The compositions of complexes were determined, and their stepwise stability constants were calculated. The oxobromide rhenium(V) complexes were shown to have higher stabilities than similar oxochloride complexes.

Potentiometric and Thermodynamic Studies of Binary and Ternary Transition Metal(II) Complexes of Imidazole-4-acetic Acid and Some Bio-relevant Ligands

Proton–ligand association constants of imidazole-4-acetic acid (IMA) were determined potentiometrically in aqueous solution at different temperatures in the range 15–35 °C. The stepwise stability constants of IMA with some selected bivalent transition metal ions were also determined in 0.1 mol·dm−3 NaNO3. The stability of the complexes follows the trend Cu2+ > Ni2+ > Co2+ > Mn2+, which is in agreement with the Irving–Williams order of the metal ions. The thermodynamic parameters for Cu(II)–IMA complex formation were derived and discussed. The ternary complexes Cu(IMA)L (IMA = imidazole-4-acetic acid, HL = amino acid, amides or DNA constituents) have been investigated. Ternary complexes of amino acids or amides are formed by a simultaneous mechanism. Amino acids form the complex Cu(IMA)L, whereas amides form two complex species Cu(IMA)L and Cu(IMA)(LH−1). The DNA constituents form both 1:1 and 1:2 complexes. The stabilities of ternary complexes are quantitatively compared with their corresponding binary complexes. The concentration distribution of the complexes in solution was evaluated as a function of pH.

An experimental study of hydrolytic behavior of thulium in basic and near-neutral solutions

Hydrolytic equilibria of Tm (III) in KOH solutions were studied at 25°C. A spectrophotometry with m-cresol purple and 2-naphthol as pH indicators was used at an ionic strength of not more than 0.0005. The results indicate that in freshly prepared solutions at pH ranging between 6 and 10 Tm is present as , , and . The stepwise stability constants of hydroxide complexes calculated at zero ionic strength were obtained as coefficient of linear regression equations from the graph of optical densities of the indicators in Tm solutions at varying pH.

Interaction of tetravalent actinides and Np(V) with some hydroxy carboxylic acids

Interaction of actinides(IV) with hydroxyisobutyric acid (HHIB) in aqueous solutions and in the course of crystallization of solid compounds was studied. The complexes MLn(4-n)+ (M = U, Np, Pu; L− is hydroxyisobutyrate anion; n = 1, 2, 3) exist in solution. Their apparent stepwise stability constants K′i were measured, and the overall concentration stability constants β3 of the complexes ML3+ were calculated. For U(IV) and Np(IV), logβ3 is close to 13.3–13.4, and for Pu(IV), logβ3 = 14.5 ± 0.9 (ionic strength I = 0.1–0.3). In the course of crystallization in air, complexes of U(IV) with hydroxyisobutyric acid, as well as those with citric acid, undergo oxidative degradation, which can be accompanied by complete oxidation of U(IV). The crystalline compounds formed in the process are oxalates of U(IV) or U(VI). The complexation of Np(V) with HHIB was studied. NpO2+ forms with HHIB the complexes NpO2L and NpO2L2−. Their concentration stability constants are logK1 = 2.04 ± 0.15 and logK2 = 0.71 ± 0.10 (I = 0.4), i.e., logβ2 = 2.75 ± 0.25.

Synthesis, characterization, biological activity and equilibrium studies of metal(II) ion complexes with tridentate hydrazone ligand derived from hydralazine

In the present study, a new hydrazone ligand (2-((2-phthalazin-1-yl)hydrazono)methyl)phenol) prepared by condensation of hydralazine (1-Hydralazinophthalazine) with salicylaldehyde (SAH). The synthesized SAH-hydrazone and its metal complexes have been characterized by elemental analyses, IR, 1H NMR, solid reflectance, magnetic moment, molar conductance, mass spectra, UV–vis and thermal analysis (TGA). The analytical data of the complexes show the formation of 1:1 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated hydrazone ligand. IR spectra show that SAH is coordinated to the metal ions in a tridentate manner through phthalazine-N, azomethine-N and phenolic-oxygen groups. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. Proton-ligand association constants of (SAH) and the stepwise stability constants of its metal complexes are determined potentiometrically in 0.1M NaNO3 at different temperatures and the corresponding thermodynamic parameters were derived and discussed. The order of −ΔG° and −ΔH° were found to obey Mn2+<Co2+<Ni2+<Cu2+, in accordance with the Irving–Williams order. The complexes were stabilized by enthalpy changes and the results suggest that the complexation is an enthalpy-driven process. The concentration distribution diagrams of the complexes are evaluated.

분광학을 이용한 흄산의 모델 리간드인 2,6-Dihydroxybenzoic acid와 우라늄(VI)의 착물형성 반응에 관한 연구

In this study the complex formation reactions between uranium(VI) and 2,6-dihydroxybenzoate (DHB) as a model ligand of humic acid were investigated by using UV-Vis spectrophotometry and time-resolved laser-induced fluorescence spectroscopy (TRLFS). The analysis of the spectrophotometric data, i.e., absorbance changes at the characteristic charge-transfer bands of the U(VI)-DHB complex, indicates that both 1:1 and 1:2 (U(VI):DHB) complexes occur as a result of dual equilibria and their distribution varies in a pH-dependent manner. The stepwise stability constants determined (log K1 and log K2) are 12.4 0.1 and 11.4 0.1. Further, the TRLFS study shows that DHB plays a role as a fluorescence quencher of U(VI) species. The presence of both a dynamic and static quenching process was identified for all U(VI) species examined, i.e., UO2 2+ , (UO2)2(OH)2 2+ , and (UO2)3(OH)5 + . The fluorescence intensity and lifetimes of each species were measured from the time-resolved spectra at various ligand concentrations, and then analyzed based on Stern-Volmer equations. The static quenching constants (log Ks) obtained are 4.2 0.1, 4.3 0.1, and 4.34 0.08 for UO2 2+ , (UO2)2(OH)2 2+ , and (UO2)3(OH)5 + , respectively. The results of Stern-Volmer analysis suggest that both mono- and bi-dentate U(VI)-DHB complexes serve as ground- state complexes inducing static quenching.

Synthesis, spectroscopic characterization, pH-metric and thermal behavior on Co(II) complexes formed with 4-(2-pyridyl)-3-thiosemicarbazide derivatives

Four new cobalt (II) complexes of some thiosemicarbazides have been synthesized and spectrochemically characterized. The thiosemicarbazides are prepared by the addition of 4-(2-pyridyl)-3-thiosemicarbazide to phenyl isothiocyanate (H 2PPS), benzoyl isothiocyanate (H 2PBO), phenyl isocyanate (H 2APO) and 2-pyridyl isothiocyanate (H 2PPY). The complexes are characterized by elemental analysis, spectral (IR, 1H NMR and UV–Vis), thermal and magnetic measurements. The studies revealed that structures of complexes are of two types octahedral and tetrahedral. The octahedral complexes are of H 2PPS, which acts as di-anionic tetradentate SSNN and H 2APO acts as mono-anionic tridentate NON. The tetrahedral complexes are of H 2PBO, which acts as di-anionic tridentate NSO and H 2PPY acts as mono-anionic bidentate NS. From the modelling studies, the bond length, bond angle, HOMO, LUMO and dipole moment had been calculated to confirm the geometry of the ligands and their investigated complexes. From TG and DTA studies kinetic parameters are determined using Coats–Redfern and Horowitz–Metzger methods. From pH metric studies at 298, 303 and 308 K and μ (0.1, 0.15 and 0.2) in 50% dioxane–water mixture the protonation constants of the ligands, the stepwise stability constants of the complexes and their thermodynamic parameters are calculated.

Inclusion complexation of chloropropham with β-cyclodextrin: Preparation, characterization and molecular modeling

An inclusion complex between the agrochemical chloropropham (CIPC) and β-cyclodextrin (β-CD) was prepared. A 2:1 host–guest stoichiometry was conformed by elemental analysis. From the phase solubility studies, the calculated stepwise stability constants were K 1 = 224.6 L/mol and K 2 = 939.2 L/mol, respectively. FT-IR, thermoanalysis and 1H NMR spectra were applied to characterize the complex. It was speculated that the inclusion mode was two β-CD cavities included the chlorophenyl and the isopropyl moiety of one CIPC molecule, which was in agreement with the most predominant configuration optimized by molecular modeling. By complexation with β-CD, the water solubility and the thermal stability of CIPC were prominently improved.