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Formation Constants (formation + constant)

Distribution by Scientific Domains
Chemistry92%

Kinds of Formation Constants

  • complex formation constant
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    Selected Abstracts

    Modeling l-dopa purification by chiral ligand-exchange chromatography

    AICHE JOURNAL, Issue 3 2007
    Nooshafarin Sanaie
    Abstract A model describing elution-band profiles that combines multiple chemical equilibria theory with the nonideal equilibrium,dispersion equation for solute transport is used to predict and characterize the separation of l,d-dopa by chiral ligand-exchange chromatography (CLEC). Formation constants and stoichiometries for all equilibrium complexes formed in the interstitial volume and pore liquid are taken from standard thermodynamic databases and independent potentiometric titration experiments. Formation constants for complexes formed with the stationary phase ligand (N-octyl-3-octylthio-d-valine) are determined from potentiometric titration data for a water-soluble analogue of the ligand. This set of pure thermodynamic parameters is used to calculate the spatially discretized composition of each column volume element as a function of time. The model includes a temperature-dependent pure-component parameter, determined by regression to a single elution band for the pure component, that corrects for subtle effects associated with immobilizing the N-octyl-3-octylthio-d-valine ligand onto the stationary phase. The model is shown to accurately predict elution chromatograms and separation performance as a function of key column operating variables. The model is then used to better understand the connection between chemical equilibria within the system and changes in band profiles and band separation resulting from changes in column operating conditions. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source]

    Lower Rim Substituted p-tert -Butyl-Calix[4]arene.

    ELECTROANALYSIS, Issue 17-18 2009

    Abstract Tetrasubstituted p-tert- butylcalix[4]arene-thioamides (1,5) were applied as ionophores in ion-selective membrane electrodes (ISE) and were tested towards Pb-selectivity. The selectivity coefficients of the electrodes were determined. The tertiary calix[4]thioamides (1, 2) show remarkable selectivity for Pb(II) cations when compared with respectable calix[4]amides. The electrode membranes with those ligands are stable, the Pb-characteristics are close to nernstian within a wide linear range (,log c=6,1). Compounds 3,5, the secondary calix[4]thioamides form less stable electrode membranes. Complex formation constants of the ligands 1, 2, 3 and 5 with Pb(II) and some most interfering ions were determined. [source]

    Development of a Novel Automatic Potentiometric System for Determination of Selenium and Its Application in Pharmaceutical Formulations and Anodic Slime

    ELECTROANALYSIS, Issue 9 2008
    Ayman
    Abstract Poly(vinyl chloride) polymeric membrane sensors containing Sn(IV) phthalocyanine dichloride (SnPC) and Co(II) phthalocyanine (CoPC) as novel electroactive materials dispersed in o -nitrophenyl octylether (o -NPOE) as a plasticizer are examined potentiometrically with respect to their response toward selenite (SeO32,) ions. Fast Nernstian response for SeO32, ions over the concentration ranges 7.0×10,6,1.0×10,3 and 8.0×10,6,1.0×10,3 mol L,l at pH,3.5,8.5 with lower detection limit of 5.0×10,6 and 8.0×10,6 mol L,1 and calibration slopes of ,25.4 and ,29.7,mV decade,1 are obtained with SnPC and CoPC based membrane sensors, respectively. The proposed sensors reveals by the modified separate solution method (MSSM) a good selectivity over different anions which differ significantly from the classical Hofmeister series. A segmented sandwich membrane method is used to determine complex formation constants of the ionophores in situe in the solvent polymeric sensing membranes. Membrane incorporating CoPC in a tubular flow detector is used in a two channels flow injection set up for continuous monitoring of selenite at a frequency of ca. 50 samples h,1. Direct determination of selenium in pharmaceutical formulations and anodic slime gives results in good agreement with data obtained using standard ICP method. [source]

    Effect of alkali metal hydroxides on the enantioseparation of amines using di- O -isopropylidene-keto- L -gulonic acid as the selector in NACE

    ELECTROPHORESIS, Issue 22 2006
    Ylva Hedeland Dr.
    Abstract The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (,)-2,3:4,6-di- O -Isopropylidene-2-keto- L -gulonic acid ((,)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (,)-DIKGA, for Li+, Na+ and Cs+ with (,)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. [source]

    Water-Soluble Sal2en- and Reduced Sal2en-Type Ligands: Study of Their CuII and NiII Complexes in the Solid State and in Solution

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 14 2006
    Isabel Correia
    Abstract The CuII and NiII complexes of the Schiff base pyr2en [N,N, -ethylenebis(pyridoxyliminato)] and reduced Schiff bases Rpyr2en [N,N, -ethylenebis(pyridoxylaminato)] and R(SO3,sal)2en (SO3,sal = salicylaldehyde-5-sulfonate) were prepared and characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy. The structure of Ni(pyr2en)·3H2O was determined by single-crystal X-ray diffraction. The pyr2en2, ligand is coordinated through two phenolate-O and imine-N atoms, in a distorted square-planar geometry. The complexation of CuII and NiII with Rpyr2en in aqueous solution is studied by pH-potentiometry, UV/Vis spectroscopy, as well as by EPR spectroscopy for the CuII system, and 1H NMR spectroscopy for the NiII system. Complex formation constants were determined and binding modes proposed. While for the CuII system all complexes present a 1:1 stoichiometry with different protonation states, for the NiII system the 2:1 (L/M) complexes become important in the basic pH range at a higher ligand excess. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    X-ray Crystal Structure and Characterization in Aqueous Solution of{N,N,-Ethylenebis(pyridoxylaminato)}zinc(II)

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006
    Isabel Correia
    Abstract The complexation of ZnII with H2Rpyr2en [H2Rpyr2en = N,N,-ethylenebis(pyridoxylaminato)] in aqueous solution has been studied by pH potentiometry and 1H NMR spectroscopy. Complex formation constants are determined and binding modes proposed. Complex formation starts at around pH 4, and several species with a 1:1 ligand-to-metal ratio with different protonation states form up to pH 12. Only above pH 10 does a hydrolytic species [ZnLH,1], become important. The crystal and molecular structures of [ZnCl(H2Rpyr2en)]+Cl,·1.5H2O (1) have been determined by X-ray diffraction. The coordination of the H2Rpyr2en ligand involves the two phenolate-O and two amine-N atoms in a distorted square-pyramidal geometry. The two pyridine-N atoms are protonated, and a Cl, atom completes the coordination sphere. Upon coordination, both N-amine atoms of H2Rpyr2en become stereogenic centres, and in both molecules of the unit cell of 1 one of the N-amine donors has an (R)-configuration, and the other an (S)-configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

    Structure Comparison of Early and Late Lanthanide(III) Homodinuclear Macrocyclic Complexes with the Polyamine Polycarboxylic Ligand H8OHEC

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004
    Ulrike A. Böttger
    Abstract The solid-state structures of two new homodinuclear chelate complexes with the late lanthanide(III) ions Yb and Lu, [Na2(Yb2OHEC)].14.5H2O (1), and [Na2(Lu2OHEC)].14.5H2O (2) (H8OHEC = 1,4,7,10,14,17,20,23-octaazacyclohexacosane- 1,4,7,10,14,17,20,23-octaacetic acid), have been determined by X-ray crystal structure analysis. Each lanthanide(III) ion is coordinated by eight donor atoms of the ligand and the geometry of the coordination polyhedron approaches a bicapped trigonal prism. These structures are compared with those of the homodinuclear chelate complexes with the same ligand and the mid to early lanthanide(III) ions Gd, Eu, La and also Y. A distinctive structural change occurs across the lanthanide series. The centrosymmetric mid to early lanthanide(III) complexes are all ninefold-coordinated in a capped square antiprismatic arrangement with a water molecule coordinated in a prismatic position. This structure is maintained in aqueous solution, together with an asymmetric minor isomer. The late lanthanide(III) OHEC complexes not only lack the inner-sphere water, but the change of coordination sphere also results in a loss of symmetry of the whole complex molecule. The observed change of coordination mode and number of the lanthanide ion may offer a geometric model for the isomerization process in eight- and ninefold-coordinated complex species that are isomers in a possible coordination equilibrium observed by NMR in aqueous solution. This model may also explain the intramolecular rearrangements necessary during water exchange in the inner coordination sphere of the complex [(Gd2OHEC)(H2O)2]2, through a slow dissociative mechanism. Protonation constants of the H8OHEC ligand and complex formation constants of this ligand with GdIII, CaII, CuII and ZnII have been determined by solution thermodynamic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Hydrolysis of diphenylmethyltin(iv) chloride in different aqueous solutions of ethanol

    HETEROATOM CHEMISTRY, Issue 7 2008
    Sima Mehdizadeh
    The hydrolysis of [(Ph)2MeSn(IV)]+ has been studied spectrophotometrically at 25,C and constant ionic strength of 0.1 mol dm,3 sodium perchlorate. Over a wide pH range, 1,11, the investigation has been performed in different aqueous solutions of ethanol. The species formed together with their formation constants have been determined using the computer program Squad. The hydrolysis constants at different media were analyzed in terms of Kamlet and Taft's parameters. A single-parameter correlation of the formation constants, K1-1 and K1-2, versus , (hydrogen-bond donor acidity), , (hydrogen-bond acceptor basicity), and ,* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work, we have also used the normalized polarity parameter, E, alone and in combination with the Kamlet,Taft's parameters to find a better correlation of the formation constants in different aqueous solutions of ethanol. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:654,660, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20484 [source]

    Peculiar kinetics of the complex formation in the iron(III),sulfate system

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2008
    Balázs Kormányos
    The results of comprehensive equilibrium and kinetic studies of the iron(III),sulfate system in aqueous solutions at I = 1.0 M (NaClO4), in the concentration ranges of T = 0.15,0.3 mM, and at pH 0.7,2.5 are presented. The iron(III),containing species detected are FeOH2+ (=FeH,1), (FeOH) (=Fe2H,2), FeSO, and Fe(SO4) with formation constants of log , = ,2.84, log , = ,2.88, log , = 2.32, and log , = 3.83. The formation rate constants of the stepwise formation of the sulfate complexes are k1a = 4.4 × 103 M,1 s,1 for the step and k2 = 1.1 × 103 M,1 s,1 for the step. The mono-sulfate complex is also formed in the reaction with the k1b = 2.7 × 105 M,1 s,1 rate constant. The most surprising result is, however, that the 2 FeSO, Fe3+ + Fe(SO4) equilibrium is established well before the system as a whole reaches its equilibrium state, and the main path of the formation of Fe(SO4) is the above fast (on the stopped flow scale) equilibrium process. The use and advantages of our recently elaborated programs for the evaluation of equilibrium and kinetic experiments are briefly outlined. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 114,124, 2008 [source]

    Kinetics and mechanism of oxidation of a ternary complex involving dipicolinatochromium(III) and DL -aspartic acid by N -bromosuccinimide

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 7 2004
    Hassan A. Ewais
    The kinetics of oxidation of [CrIII(Dpc)(Asp)(H2O)2] (Dpc = dipicolinic acid and Asp = DL -aspartic acid) by N -bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: where k2 is the rate constant for the electron transfer process, K1 is the equilibrium constant for deprotonation of [CrIII(Dpc)(Asp)(H2O)2], K2 and K3 are the pre-equilibrium formation constants of precursor complexes [CrIII(Dpc)(Asp)(H2O)(NBS)] and [CrIII(Dpc)(Asp)(H2O)(OH)(NBS)],. Values of k2 = 4.85 × 10,2 s,1, K1 = 1.85 × 10,7 mol dm,3, and K2 = 78.2 mol,1 dm3 have been obtained at 30°C and I = 0.1 mol dm,3. The experimental rate law is consistent with a mechanism in which the deprotonated [CrIII(Dpc)(Asp)(H2O)(OH)], is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 394,400, 2004 [source]

    Theoretical studies on the structure and protonation of Cu(II) complexes of a series of tripodal aliphatic tetraamines: Good correlations with the experimental data

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2010
    Sadegh Salehzadeh
    Abstract DFT(B3LYP) studies on first protonation step of a series of Cu(II) complexes of some tripodal tetraamines with general formula N[(CH2)nNH2][(CH2)mNH2][(CH2)pNH2] (n = m = p = 2, tren; n = 3, m = p = 2, pee; n = m = 3, p = 2, ppe; n = m = 3, tpt; n = 2, m = 3, p = 4, epb; and n = m = 3, p = 4; ppb) are reported. First, the gas-phase proton macroaffinity of all latter complexes was calculated with considering following simple reaction: [Cu(L)]2+(g) + H+(g) , [Cu(HL)]3+(g). The results showed that there is a good correlation between the calculated proton macroaffinities of all complexes with their stability constants in solution. Then, we tried to determine the possible reliable structures for microspecies involved in protonation process of above complexes. The results showed that, similar to the solid state, the [Cu(L)(H2O)]2+ and [Cu(HL)(H2O)2]3+ are most stable species for latter complexes and their protonated form, respectively, at gas phase. We found that there are acceptable correlations between the formation constants of above complexes with both the , and , of following reaction: [Cu(L)(H2O)]2+(g) + H+(g) + H2O(g) , [Cu(HL)(H2O)2]3+(g). The , of the latter reaction can be defined as a theoretically solvent,proton macroaffinity of reactant complexes because they have gained one proton and one molecule of the solvent. The unknown formation constant of [Cu(epb)]2+ complex was also predicted from the observed correlations. In addition, the first proton affinity of all complexes was studied in solution using DPCM and CPCM methods. It was shown that there is an acceptable correlation between the solvent,proton affinities of [Cu(L)(H2O)]2+ complexes with formation constants of [Cu(HL)(H2O)2]3+ complexes in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

    Structure-stability correlations for imine formation in aqueous solution

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 10 2005
    C. Godoy-Alcántar
    Abstract Imine formation between 25 aldehydes and 13 amines in aqueous solution in the pH range 7,11 was studied by 1H NMR spectroscopy. A three-parameter linear equation correlating logarithms of imine formation constants with pKa and HOMO energies of amines and LUMO energies of aldehydes is proposed. In view of the widespread occurrence of imine-forming processes in both chemistry and biology, the data presented are of significance for physical organic chemistry and of particular interest for dynamic combinatorial chemistry. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Sequestration of organometallic compounds by natural organic matter. binding of trimethyltin(IV) by fulvic and alginic acids

    APPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2006
    Alba Giacalone
    Abstract The binding capacity of fulvic and alginic acids towards trimethyl tin(IV) cation was quantitatively determined in order to evaluate the sequestering ability of toxic organometallic compounds by natural organic matter. Investigations were performed in the pH range of natural waters (5,8.5) where the carboxylate groups, largely present in both sequestering agents, are the main binding sites. A chemical interaction model, according to which both the protonation of polyelectrolyte ligands and the hydrolysis of the organotin cation in NaCl aqueous solution were considered, was used to define the speciation of the systems under investigation. Measurements performed at different ionic strength values (0.1, 0.25, 0.5 and 0.7 mol L,1, NaCl) allowed us to consider the dependence of stability constants on the ionic strength, and to calculate the formation constants at infinite dilution. Results obtained show the formation of the complex species TMT(L), TMT(L)2 and TMT(L)(OH) for L = fulvic acid and TMT(L) for L = alginic acid, respectively. In order to compare the strength of interaction of these natural poly electrolytes with other analogous synthetic polyelectrolytes, measurements were also carried out on the trimethyltin(IV),polyacrylate (5.1 kDa) system, and in this case the formation of TMT(L), TMT(L)2 and TMT(L)(OH) species was found. Results show the following trend of stability for the species TMT(L) in the systems investigated: TMT,fulvate , TMT,polyacrylate > TMT,alginate. On the basis of the stability data obtained, the lowest concentration of fulvic and alginic acids, able to act as sequestering agents towards triorganotin(IV) cation in the conditions of natural waters, was also calculated. Copyright © 2006 John Wiley & Sons, Ltd. [source]