Equilibrium Constants For Formation Of Complexes Research Articles

Protonation constants of endo- and exogenous L-amino acids and their derivatives in aqueous and mixed solution: Unraveling molecular secrets.

The aim of this review is to summarize the progress made in the determination of the protonation constants of biologically active ligands: endo- and exogenous L-amino acids and their derivatives in aqueous and mixed solutions using different experimental techniques. The knowledge of the protonation constants of the aforementioned ligands is crucial for the determination of the equilibrium constants of complex formation and thus for the understanding of complex biological reactions such as transamination, racemization, and decarboxylation. Thus, the protonation constants of ligands are a measure of their ability to form complexes with metal ions. This knowledge not only helps to understand fundamental biochemical processes, but also has practical applications in areas such as drug design, where ligands are often targeted for therapeutic purposes. The activity of the ligands tends to increase after complexation and their order is consistent with the values of the stepwise dissociation constants of the complexes formed. Understanding the properties of ligands by determining their protonation constants in different environments and their interactions with surrounding molecules is crucial to unraveling the complexity of biological systems.

Interaction of Salicylamide and Salicylic Acid with Iron and Cobalt and their Comparative Study by IR and NMR

The complexes formed by salicylic acid and several substituted derivatives of salicylic acid (Salicylamide) with essential metal ions of the soil (iron and cobalt) have been investigated at 25° and in a medium of variable ionic strength using pH. The equilibrium constants of complex formation of the 1 : 1 , 1 : 2 and1 : 3 mole ratio metal–acid complexes formed are discussed with reference to the activity degradation of substituents. Salicylic acid and Salicylamide after disposal can also react with the various metal ions present in the soil to form complexes. The rate at which these complexes are formed is done with the help of UV-vis. Spectroscopy. The complexes formed are characterized by various Spectroscopic technique viz. FTIR and NMR.

Investigation of manganese(II)-insulin complexes using electrospray ionization mass spectrometry

Manganese is a trace element in human nutrition. It is involved in many enzymes, proteins and biological activities. Mn(II) ion has the capable of binding to protein or peptides. Insulin is a blood glucose-lowering peptide hormone and it is secreted by the pancreatic β-cells. In this study, the binding capability of Mn(II) ions to insulin was studied using ESI-MS, nano-ESI-MS and MS/MS methods. The binding of Mn(II) ions to insulin molecule was studied by examining the effect of pH, the molar ratio of Mn(II) ions to insulin, the flow rate with nano-ESI system and MS/MS spectrometry. The ESI-MS measurements showed that the Mn(II)-insulin complexation mostly produces ML and M2L type complexes. The highest binding ratio was found at pH 7. The complex formation equilibrium constants of Mn(II)-insulin were calculated as Kf1: 1.03 ± 0.12 × 104 and Kf2: 1.93 ± 0.17 × 103. The nano-ESI-MS and MS/MS measurements exhibited strong and specific binding of Mn(II) ions to insulin molecule. It was concluded from all the ESI-MS measurements that Mn(II) ion has a high affinity to insulin molecule to form stable complexes.

Levaquin drug complexing property towards platinum and palladium metal ions: Thermodynamic studies in aqueous solutions

The experimental protonation and complex formation equilibrium constants of levaquin (LFX) with platinum(II) and palladium(II) metal ions have been investigated at 310.15K in water solutions at ionic strength of I=0.16mol·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of LFX and the equilibrium constants of its binary complexes with the studied platinum(II) and palladium(II) metal ions in I=0.16mol·dm−3 NaNO3 water solutions were observed at different temperatures such as 298.15, 310.15, 318.15 and 328.15K. The theoretical calculations of overall protonation and stability constants of the metal ion-LFX complex species in aqueous solutions were predicted as the free energy change associated with the LFX protonation, and metal ion – LFX complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The determination of equilibrium constants were confirmed by the spectrophotometric method with the refinement by using the HypSpec program. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -LFX). Precisely, this theoretically predications could be useful to control the most real protonation constants of levaquin ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different platinum(II) and palladium(II) metal ions towards LFX in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - LFX complex species in solutions were estimated using HySS 2009 software.

Thermodynamic studies on metal ions – Ninhydrin – Glycine interactions in aqueous solutions

The experimental protonation and complex formation equilibrium constants of ligands (ninhydrin (NHN) and glycine (Gly)) with trivalent (iron(III), aluminium(III), and chromium (III)), divalent (copper(II), cobalt(II), nickel(II), strontium(II), manganese(II), and mercury(II)) and monovalent silver(I) metal ions have been investigated at 310.15 K in water solutions at ionic strength of 13.60 g·dm−3 NaNO3 using pH-potentiometric, UV–visible spectrophotometric, and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NHN and the equilibrium constants of its binary complexes and ternary complexes with the studied metal ions in 13.60 g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-ninhydrin complex species in aqueous solutions were predicted as the free energy change associated with the ninhydrin protonation, and metal ion – ninhydrin – glycine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modelling. The convention of the experimental Potentiometry/Spectrophotometry techniques and theoretical calculations provide a complete picture of the microscopic equilibria of the studied metal ions – ninhydrin – glycine systems. Precisely, this theoretical predication could be useful to control the most real protonation constants of ninhydrin and glycine ligands in which the binding sites change due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards ninhydrin and glycine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions – ninhydrin – glycine complex species in solutions were estimated using HySS 2009 software.

Dimethyl Sulfoxide Complexes Detected at Ambient Conditions.

Dimethyl sulfoxide (DMSO) is an important intermediate in the atmospheric oxidation of dimethyl sulfide (DMS). DMS, emitted from the ocean, is the main natural sulfur source, and its oxidation products are essential in the formation of sulfate aerosols. The high atmospheric concentration of water makes hydrogen bonding with DMS and its oxidation products likely. Through hydrogen bonding, water can potentially catalyze and affect the steps of the oxidation. We investigate binary hydrogen-bound complexes involving DMSO. Both water·DMSO and methanol·DMSO complexes are identified in an Ar matrix, and at room temperature, a Gibbs free energy of 0.7 kJ/mol for the formation of the methanol·DMSO complex is determined. Assuming a similar Gibbs free energy of the hydrate, it would suggest a relatively high abundance of the DMSO hydrate relative to the monomer in the atmosphere. The effect of changing the atom divalently bound to the hydrogen bond accepting oxygen, from S to C (DMSO to acetone), is found to significantly decrease the equilibrium constant of complex formation.

Effect of temperature and solvent properties on the process of complex formation between crown ether 15C5 and Na+ in the (propan-1-ol + water) mixture at temperatures from T = 293.15 K to T = 308.15 K

Thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na+) in the mixtures of propan-1-ol (PrOH) with water (W) at different temperatures have been calculated. To obtain this function two experimental methods have been used. The equilibrium constants of complex formation (15C5/Na+) have been determined by conductivity measurements and the enthalpic effect of complex formation has been measured by the calorimetric method and has been also calculated using van’t Hoff’s equation. The complexes are enthalpy stabilized but entropy destabilized. Effect of solvent properties on the process of complex 15C5/Na+ formation in PrOH+W mixtures has been discussed. The obtained results were compared with analogous data in the mixtures of water with methanol or ethanol and discussed.

Nicotine – Metal ion interactions in solutions: Potentiometric, cyclic voltammetry investigations and quantum chemical calculations

The experimental protonation and complex formation equilibrium constants of nicotine (NIC) with trivalent (iron (III), and chromium (III)) and divalent (copper (II), and nickel (II)) metal ions have been investigated at 310.15 oK in water solutions at ionic strength of 13.60g·dm−3 NaNO3 using pH-potentiometric and cyclic voltammetry techniques, and by means of Hyperquad 2008 estimation model program. Also, the dissociation constants of NIC and the equilibrium constants of its binary complexes with the studied metal ions in 13.60g·dm−3 NaNO3 water solutions were observed at different temperatures such as (298.15, 310.15, 318.15 and 328.15) K. The theoretical calculations of overall protonation and stability constants of the metal ion-nicotine complex species in aqueous solutions were predicted as the Gibbs energy change associated with the nicotine protonation, and metal ion – nicotine complex formation equilibria using ab initio and density function theory calculations by applying Gaussian 09 software molecular modeling. The usage of the experimental potentiometry/spectrophotometry techniques and theoretical predictions provides a complete picture of the microscopic equilibria of the studied systems (metal ions -nicotinate). Precisely, this theoretically predications could be useful to control the most real protonation constants of nicotine ligand in which the binding sites changes due to the ligand protonation/deprotonation equilibria. Also, the complexing capacities of different metal ions towards nicotine in solutions were evaluated and discussed. From the determined experimental stability constants of different metal complex species, the concentration distribution diagrams of the various metal ions - nicotine complex species in solutions were estimated using HySS 2009 software.

Theoretical study of charge transfer complexes between antithyroid thioamides and TCNE: Thermodynamics of the complex formation

Thermodynamic characteristics of charge transfer complexes formed between both mono and bicyclic thioamides as donors and tetracyanoethylene have been studied by selected density functional theory and wave-function based methods combined with the polarizable continuum model. The thioamide derivatives are known to exhibit significant antithyroid activity. The equilibrium constants of complex formation (K) derived from calculated thermodynamic parameters nicely correlate with the donor strength while their experimental counterparts reveal practically no correlation. Based on theoretical calculations we conclude that the rather erratic behavior of the experimental K values is related to the presence of chemical reactions including radical ions formation, which proceed along with the π-complex formation.

Secrets of solid state and aqueous solution structures of [Ni(tmdta)](2-).

The molecular structures of Li2[Ni(tmdta)]·5H2O (1a, tmdta = trimethylenediaminetetraacetate), {C(NH2)3}2[Ni(tmdta)]·6H2O (1b), and {Ni(H2O)6}[Ni(tmdta)]·2H2O (2a) have been determined. The central trimethylenediamine chelate ring shows half-chair (hc) geometries in 1a and 1b, while a twist-boat (tb) conformation is encountered in 2a. The coexistence of tb and hc forms in the solid state prompted us to elucidate the existence of a tb ⇌ hc equilibrium in aqueous solution. Evaluation of the data from solid state vibrational spectra (Raman and IR) for the hc and tb forms showed excellent agreement with simulated spectra obtained with DFT computations (TPSSh/TZVP). This outstanding matching between theory and experiment enabled us to build composite spectra with varying hc:tb ratios. Comparison of these results with Raman and IR spectra recorded for [Ni(tmdta)](2-) in aqueous solution revealed that simulated Raman and IR spectra with a hc:tb ratio = 2:3 match the solution spectra in an accurate way. This equilibrium ratio enabled us to compute (13)C NMR sifts for the paramagnetic solution spectrum of [Ni(tmdta)](2-) based on the relative contributions by hc and tb fractions. This leads to computed shifts that agree closely with the experimental ones. Also, the kinetics of the skeleton dynamics could be estimated quantitatively by temperature-dependent (13)C NMR spectroscopic measurements. An interesting effect encountered for the very first time here concerns a drastic intensity difference of the 10Dq band ((3)A2g → (3)T2g(F) transition) in solid state electronic spectra of tb vs hc isomers, where the intensity of this band in the case of the hc form is much lower than that of the tb conformer and thus more similar to the case of the usual Ni(II) chromophore in octahedral environment. The equilibrium constants for complex formation and protonation of Ni(II)-tmdta at low pH have been estimated by pH-dependent UV-vis titration experiments. Correlation of these data with those of Ni(II)-edta and related 3d M(II) edta and tmdta complexes allow important conclusions on the consequences resulting from extending the central diamine ring in the ligand by one methylene group in terms of both complex and protolytic stability for edta vs tmdta complexes.

NMR study of the complex formation between tert-butyl hydroperoxide and tetraalkylammonium bromides

The interaction between tert-butyl hydroperoxide and tetraalkylammonium bromides was studied by NMR spectroscopy in acetonitrile-d 3 at 298 K. The complex formation between the hydroperoxide molecule and corresponding quaternary ammonium salt was experimentally proven. The equilibrium constants of complex formation were determined by both 1H and 13C NMR spectroscopy. Complex stability decreases with increasing intrinsic volume of the tetraalkylammonium cation. .

Effect of temperature on the process of complex formation crown ether 15C5 with Na+ in the (water + ethanol) mixture at temperatures from (293.15 to 308.15) K

• The system 15C5/Na + complex + water + ethanol has been investigated. • The thermodynamic functions of 15C5/Na + complex formation were calculated. • The enthalpy of complex formation has been calculated using calorimetric method. • The enthalpy of complex formation has been calculated from van’t Hoff's equation. • The obtained results have been compared. Thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na + ) in the mixtures of water (W) with ethanol (EtOH) at different temperatures have been calculated. To obtain this function two experimental methods have been used. The equilibrium constants of complex formation have been determined by conductivity measurements and the enthalpic effect of complex formation has been measured by the calorimetric method and has been also calculated using van’t Hoff's equation. The obtained results were compared and discussed. The complexes are enthalpy stabilized but entropy destabilized.

Effect of temperature on the process of complex formation crown ether 15C5 with Na+ in the mixture of water with methanol

Thermodynamic functions of complex formation of 15-crown-5 ether (15C5) with sodium cation (Na+) in the mixtures of water (W) with methanol (MeOH) at different temperature have been calculated. To obtain this function two experimental methods have been used. The equilibrium constants of complex formation have been determined by conductivity measurements and the enthalpic effect of complex formation has been measured by the calorimetric method and has been also calculated using van’t Hoff’s equation. The obtained results were compared and discussed. The complexes are enthalpy stabilized but entropy destabilized.

Thermodynamic Features of Benzene-1,2-Diphosphonic Acid Complexes with Several Metal Ions

Among his many contributions to the advancement of f-element chemistry and separation science, Professor Gregory R. Choppin's research group completed numerous investigations featuring the application of distribution techniques to the determination of metal complexation equilibrium quotients. Most of these studies focused on the chemistry of lanthanide and actinide complexes. In keeping with that tradition, this report discusses the complex formation equilibrium constants for complexes of trivalent europium (Eu3+) with benzene-1,2-diphosphonic acid (H4BzDP) determined using solvent extraction distribution experiments in 0.2 M (Na,H)ClO4 media in the temperature range of 5 – 45°C. Protonation constants for HnBzDP4-n and stoichiometry and stability of BzDP4- complexes with Zn2+, Ni2+, and Cu2+ have also been determined using potentiometric titration (at I = 0.1 M) and 31P NMR spectroscopy. Heats of protonation of HnBzDPn-4 species have been determined by titration calorimetry. From the temperature dependence of the complex Eu3+-HnBzDPn-4 equilibrium constant, a composite enthalpy (ΔH = −15.1 (±1.0) kJ mol−1) of complexation has been computed. Comparing these thermodynamic parameters with literature reports on other diphosphonic acids and structurally similar carboxylic acids indicates that exothermic heats of complexation are unique to the Eu-BzDP system. Comparisons with thermodynamic data from the literature indicate that the fixed geometry imposed by the benzene ring enhances complex stability.

Thermodynamic characteristics of complex formation reactions between d- and f-elements and alkylated dipyrrolylmethene in dimethylformamide

Thermal effects of the reactions of complex formation between d- and f-elements and 3,3′,5,5′-tetramethyl-4,4′-diethyl-2,2′-dipyrrolylmethene in dimethylformamide are determined from data of titration microcalorimetry and the temperature behavior of the complex formation equilibrium constants. The entropy and free energy changes of the complex formation reactions are calculated. It is shown that enthalpy-entropy compensation is observed for complex formation processes in all cases. Contributions from the enthalpy and entropy factors to the free energy change of the complex formation are analyzed, allowing us to confirm earlier conclusions as to the effect of the nature of a complexing agent on the relative percentage of covalent and ionic characters of the M-L bond. The dependence of the complex formation enthalpies on the inverse radius of a complexing agent is revealed for the lanthanide complexes.

Thermodynamic Investigation of the Formation of Complexes between Norfloxacin and Various Mononucleotides

The fluorescence of norfloxacin was quenched by various nucleotides. The ratio of the fluorescence intensities in the absence and presence of nucleotide was linearly dependent on nucleotide concentration, suggesting that quenching occurred through the formation of nonfluorescent norfloxacin-nucleotide complexes. The gradient of the linear relationship represented the equilibrium constant of complex formation; it decreased with increasing temperature. The slopes of van’t Hoff plots constructed from the temperature-dependent equilibrium constants were positive in all cases, indicating that complex formation was energetically favorable – i.e., exothermic, with negative Gibb’s free energy. The equilibrium constant increased when triphosphate was used instead of monophosphate. It also increased when the oxygen at the C'2 position of the nucleotide was removed. Both enhancements were due to entropic effects: entropy decreased when complexes with AMP or GMP formed, while it increased when norfloxacin complexed with ATP, GTP, dAMP and dGMP.

An insight into the C–S coupling mechanism of aryl Grignard reagents with aryl arenesulfonates

The reaction rate and thermodynamic parameters in the reaction of phenylmagnesium bromide with phenyl tosylate in THF:toluene binary solvents and also in toluene were analyzed. The relative changes in the rate constants are strictly bound to changes in the equilibrium constant of complex formation between the sulfonate and the Grignard reagent by replacement of a donor THF molecule as well as the transfer rate of the carbanion to the sulfonate in the complex. These results provide another support for asynchronous SNa mechanism comprising a four-center transition state mechanism.

Complex Formation of Crown Ethers and Cations in Water−Organic Solvent Mixtures: The Thermodynamic Functions of Complex Formation of Benzo-15-crown-5 with Na+ in Water + Ethanol at 298.15 K

The enthalpies of solution of benzo-15-crown-5 ether in ethanol + water and ethanol + water + sodium iodide systems have been measured at T = 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and ethanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with a sodium cation have been determined by conductivity measurements at T = 298.15 K. In the process of complex formation, ethanol molecules show their hydrophobic properties.

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm ( λ max of [Fe(CN) 5PhNHNH 2] 3−, complex) under the optimum reaction conditions at: 2.5 × 10 −3 M [Fe(CN) 6] 4−, 1.0 × 10 −3 M [PhNHNH 2], 8.0 × 10 −7 M [Ag +], pH 2.8 ± 0.02, ionic strength ( μ) 0.02 M (KNO 3) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10 −8 M with a detection limit of 2 × 10 −9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor ( K CI), catalyst–substrate ( K s) and Michaelis–Menten constant ( K m) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XII. Effect of the Acid–Base Properties of the Mixture on the Thermodynamic Functions of Complex Formation of Benzo-15-Crown-5 with Na+ in Water–Methanol Mixtures at 298.15 K

The enthalpies of solution of benzo-15-crown-5 ether in methanol–water mixtures and methanol–water–sodium iodide systems have been measured at 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and methanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with the sodium cation have been determined by conductivity measurements at 298.15 K. The thermodynamic functions of the formation of these complexes have been calculated. The Gibbs energy of complex formation depends on the base–acid properties of methanol–water mixture.