Potentiometric study of the protonation equilibrium of Tris(Hydroxymethyl) aminomethane in aqueous sodium perchlorate solutions at 25 degrees C: construction of a thermodynamic model

The protonation equilibrium of the Tris(Hydroxymethyl)aminomethane (TRIS) has been studied using an automated potentiometric system. The temperature was kept constant at 25 degrees C and the ionic strength was 0.1, 0.5, 1.0, 2.0 and 3.0 mol dm(-3) in NaClO(4). The experimental constants, obtained at different ionic strengths, were correlated by means of the modified Bromley methodology (MBM) and the thermodynamic protonation constant found to be log (0)beta = 8.07 +/- 0.01 . Those values together with some others for NaCl medium were used to construct a thermodynamic model on both molal and molar scales for the protonation equilibrium of TRIS.     

Potentiometric study of the protonation and distribution equilibria of d-gluconic-delta-lactone acid in sodium perchlorate solutions at 25 degrees C and construction of a thermodynamic model

The protolytic behavior of d-gluconic-delta-lactone acid has been studied by means of automated potentiometric titrations at different ionic strengths in the range 0.1相似文献   

Mixed hydroxide complex formation and solubility of bismuth in nitrate and perchlorate medium

From the precipitation borderlines in the pBi'-pH diagram, determined experimentally under CO(2)-free conditions, the stability constants of bismuth hydroxide, bismuthoxynitrate and bismuthoxyperchlorate have been established. The following values have been found Nitrate-medium: Perchlorate-medium: log *K(SO)(OH) = 5.2, log *K(SO)(OH) = 5.2; log *K(SO)(NO(3)) = -1.2, log*K(SO)(ClO(4)) = -0.9; log *beta(2) = -4.0, log *beta(2) = -4.1; log *beta(3) = -10.0, log *beta(3)= -9.9; log *beta(4) = -21.5, log *beta(4) = -21.5; log *beta(1,0,1) = 1.2, log *beta(1,0,1) = 3.5. The constants refer to precipitates equilibrated for 30 min, prepared at room temperature (23 +/- 0.5 degrees) in sodium perchlorate or sodium nitrate medium with an ionic strength of 1.00 +/- 0.01. Concerning error propagation it is stated that pBi' values calculated with these constants will have a standard deviation of about 0.1 log unit.     

The study of complex equilibria of uranium(VI) with selenate

Uranyl (M)-selenate (L) complex equilibria in solution were investigated by spectrophotometry in visible range and potentiometry by means of uranyl ion selective electrode. The formation ML and ML(2) species was proved and the corresponding stability constants calculated were: log beta(1) = 1.57(6) +/- 0.01(6), log beta(2) = 2.42(3) +/- 0.01(3) (I = 3.0 mol 1(-1) Na(ClO(4), SeO(4)) (spectrophotometry) at 298.2 K. Using potentiometry the values for infinite dilution (I --> 0 mol 1(-1)) were: log beta(1) = 2.64 +/- 0.01, log beta(2) 3.4 at 298.2 K. Absorption spectra of the complexes were calculated and analysed by deconvolution technique. Derivative spectrophotometry for the chemical model determination has also been successfully applied.     

The second acidic constant of salicylic acid

The second dissociation constant of salicylic acid (H2L) has been determined, at 25 degrees C, in NaCl ionic media by UV spectrophotometric measurements. The investigated ionic strength values were 0.16, 0.25, 0.50, 1.0, 2.0 and 3.0 M. The protolysis constants calculated at the different ionic strengths yielded, with the Specific Interaction Theory, the infinite dilution constant, log beta1(0) = 13.62 +/- 0.03, for the equilibrium L2- + H+ <==> HL-. The interaction coefficient between Na+ and L2-, b(Na+, L2-) = 0.02 +/- 0.07, has been also calculated.     

Sequestering ability of polycarboxylic ligands towards dioxouranium(VI)

In this paper we report a comparison on the sequestering ability of some polycarboxylic ligands towards dioxouranium(VI) (UO(2)(2+), uranyl). Ligands taken into account are mono- (acetate), di- (oxalate, malonate, succinate and azelate), tri- (1,2,3-propanetricarboxylate) and hexa-carboxylate (1,2,3,4,5,6-benzenehexacarboxylate). The sequestering ability of polycarboxylic ligands towards UO(2)(2+) was quantified by a new approach expressed by means of a sigmoid Boltzman type equation and of a empirical parameters (pL(50)) which defines the amount of ligand necessary to sequester 50% of the total UO(2)(2+) concentration. A fairly linear correlation was obtained between pL(50) or log K(110) (log K(110) refers to the equilibrium: UO(2)(2+)+L(z-)=UO(2)L((2-z)); L=generic ligand) and the polyanion charges. In order to complete the picture, a tetra-carboxylate ligand (1,2,3,4-butanetetracarboxylate) was studied in NaCl aqueous solutions at 0相似文献   

Cyclodextrin and modified cyclodextrin complexes of E-4-tert-butylphenyl-4'-oxyazobenzene: UV-visible, 1H NMR and ab initio studies

alpha-Cyclodextrin, beta-cyclodextrin, N-(6(A)-deoxy-alpha-cyclodextrin-6(A)-yl)-N'6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea and N,N-bis(6(A)-deoxy-beta-cyclodextrin-6(A)-yl)urea (alphaCD, betaCD, 1 and 2) form inclusion complexes with E-4-tert-butylphenyl-4'-oxyazobenzene, E-3(-). In aqueous solution at pH 10.0, 298.2 K and I = 0.10 mol dm(-3)(NaClO(4)) spectrophotometric UV-visible studies yield the sequential formation constants: K(11) = (2.83 +/- 0.28) x 10(5) dm(3) mol(-1) for alphaCD.E-(-), K(21) = (6.93 +/- 0.06) x 10(3) dm(3) mol(-1) for (alphaCD)(2).E-3(-), K(11) = (1.24 +/- 0.12) x 10(5) dm(3) mol(-1) for betaCD.E-(-), K(21) = (1.22 +/- 0.06) x 10(4) dm(3) mol(-1) for (betaCD)(2).E-(-), K(11) = (3.08 +/- 0.03) x 10(5) dm(3) mol(-1) for .E-3(-), K(11) = (8.05 +/- 0.63) x 10(4) dm(3) mol(-1) for .E-3(-) and K(12) = (2.42 +/- 0.53) x 10(4) dm(3) mol(-1) for .(E-3(-))(2). (1)H ROESY NMR studies show that complexation of E-3(-) in the annuli of alphaCD, betaCD, 1 and 2 occurs. A variable-temperature (1)H NMR study yields k(298 K)= 6.7 +/- 0.5 and 5.7 +/- 0.5 s(-1), DeltaH = 61.7 +/- 2.7 and 88.1 +/- 4.2 kJ mol(-1) and DeltaS = -22.2 +/- 8.7 and 65 +/- 13 J K(-1) mol(-1) for the interconversion of the dominant includomers (complexes with different orientations of alphaCD) of alphaCD.E-3(-) and (alphaCD)(2).E-3(-), respectively. The existence of E-3(-) as the sole isomer was investigated through an ab initio study.     

Ionic strength dependence of formation constants-XVIII. The hydrolysis of iron(III) in aqueous KNO(3) solutions

The hydrolysis of iron(III) was studied potentiometrically at different ionic strengths in KNO(3) aqueous solutions, at 25 degrees C, to determine the dependence of hydrolysis constants on ionic strength (nitrate media), to check the existence of nitrate-ferric ion interactions, and to confirm the formation of high polymeric species. Under the experimental conditions 0.03 I (KNO(3)) 1M, 0.3 C 12 mM, the species Fe(OH)(2+), Fe(2)(OH)(4+)(2), Fe(OH)(+)(2) and Fe(12)(OH)(2+)(34) were found, and the hydrolysis constants log beta(11) = 2.20, log beta(12) = -2.91, log beta(22) = -5.7, log beta(12,34) = -48.9 (I = 0M) were calculated. The ionic strength dependence of hydrolysis constants is quite close to that found for several protonation and metal complex formation constants reported elsewhere.     

Characterisation of the protolytic properties of synthetic carbonate free fluorapatite

The acid/base surface properties of carbonate free fluorapatite (Ca5(PO4)3F) have been characterised using high precision potentiometric titrations and surface complex modelling. Synthetic carbonate free fluorapatite was prepared and characterised by SEM, XRD, FT-IR and FT-Raman. The specific surface area was determined to be 17.7+/-1.2 m2 g(-1) with BET (N2 adsorption). The titrations were performed at 25+/-0.2 degrees C, within the pH range 5.7-10.8, in 0.10 and 0.50 mol dm(-3) NaNO3 ionic media. Experimental data were interpreted using the constant capacitance model and the software FITEQL 4.0. The surface equilibria: [triple bond]S1OH <==> [triple bond]S1O- + H+ lg betaS(-110) (int), [triple bond]S2OH <==> [triple bond]S2O- + H+ lg betaS(-101) (int) well describes the surface characteristics of synthetic fluorapatite. The equilibrium constants obtained were: lg betaS(-110) (int) = -6.33+/-0.05 and lg betaS(-101) (int) = -8.82+/-0.06 at I = 0.10 mol dm(-3). At the ionic strength 0.50 mol dm(-3), the equilibrium constants were slightly shifted to: lg betaS(-110) (int) = -6.43+/-0.05 and lg betaS(-101) (int) = -8.93+/-0.06. The number of active surface sites, N(s), was calculated from titration data and was found to be 2.95 and 2.34 sites nm(-2) for the ionic strengths 0.10 and 0.50 mol dm(-3), respectively. pH(PZC) or the IEP was found to be 5.7 from Z-potential measurements.     

The acid stability constants of Alizarin Fluorine Blue

Two recent attempts to determine the dissociation constants of 3-aminomethylalizarin-N,N-diacetic acid are discussed and the results compared with values that can be predicted from earlier work on iminodiacetic acid derivatives and from the absorption spectra of the reagent at different pH values. Results of a potentiometric and spectrophotometric study to determine the stability constants of the various protonated species of the reagent in aqueous solution at ionic strengths 0.1 and 0.5 (potassium chloride) are: log K(H)(HL) = 12.1, log K(H)(H(2)L) = 9.81, log K(H)(H(3)L) = 5.47, log K(H)(H(4)L) = 2.54, and log K(H(2)L)(H(5)L(2)) = 2.2 at ionic strength 0.5.     

pH-metric studies on ternary metal complexes of some amino acids and benzimidazole

The stability constants of binary and ternary complexes of copper(II) and nickel(II) with some amino acids (d-histidine, dl-serine, lysine) as primary ligands and benzimidazole as a secondary ligand were determined pH-metrically. The study was conducted in 10% (v/v) ethanol-H(2)O medium and at an ionic strength of 0.1 mol dm(-3) NaNO(3) at 20 +/- 1 degrees C, Values of Delta log K were discussed on the basis of statistical considerations and the nature of the species formed. The stability of the binary and mixed ligand complexes are discussed in terms of the molecular structure of benzimidazole and the amino acids as well as the nature of the metal ion.     

Study of complex formation in the manganese(II)/azide system

The complex formation between Mn(II) cations and N(3)(-) anions was studied in aqueous medium at 25 degrees C and ionic strength 2.0 M (NaClO(4)). Data of average ligand number, n (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N(3)(-)/HN(3) system followed by integration to obtain Leden's function, F(0)(L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: beta(1)=4.15+/-0.02 M(-1), beta(2)=6.61+/-0.04 M(-2), beta(3)=3.33+/-0.02 M(-3), beta(4)=0.63+/-0.01 M(-4). A linear plot of log K(n) vs. (n-1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N(3)(-) concentration is greater than 1.0 M.     

Complexation of Nickel(II) with Guanosine 5'-Monophosphate and Inosine 5'-Monophosphate: A Potentiometric and Calorimetric Study

The constants (K(s)) and enthalpies (DeltaH(s)) for stacking interactions between purine nucleoside monophosphates were determined by calorimetry; the values thus obtained were guanosine as follows: K(s) = 2.1 +/- 0.3 M(-)(1) and DeltaH(s) = -41.8 +/- 0.8 kJ/mol for adenosine 5'-monophosphate (5'AMP); K(s) = 1.5 +/- 0.3 M(-1) and DeltaH(s) = -42.0 +/- 1.5 kJ/mol for guanosine 5'-monophosphate (5'GMP); and K(s) = 1.0 +/- 0.2 M(-1) and DeltaH(s) = -42.3 +/- 1.1 kJ/mol for inosine 5'-monophosphate (5'IMP). The interaction of nickel(II) with purine nucleoside monophosphates was studied using potentiometric and calorimetric methods, with 0.1 M tetramethylammonium bromide as the background electrolyte, at 25 degrees C. The presence in solution of the complexes [Ni(5'GMP)(2)](2)(-) and [Ni(5'IMP)(2)](2)(-) was observed. The thermodynamic parameters obtained were log K(ML) = 3.04 +/- 0.02, log K(ML2) = 2.33 +/- 0.02, DeltaH(ML) = -18.4 +/- 0.9 kJ/mol and DeltaH(ML2) = -9.0 +/- 1.9 kJ/mol for 5'GMP; and log K(ML) = 2.91 +/- 0.01, log K(ML2) = 1.92 +/- 0.01, DeltaH(ML) = -16.2 +/- 0.9 kJ/mol and DeltaH(ML2) = -0.1 +/- 2.3 kJ/mol for 5'IMP. The relationships between complex enthalpies and the degree of macrochelation, as well as the stacking interaction between purine bases in the complexes are discussed in relation to previously reported calorimetric data.     

Molecular switch triggered by solvent polarity: synthesis,Acid-base behavior,alkali metal ion complexation,and crystal structure

The synthesis and characterization of the new tetraazamacrocycle L, bearing two 1,1'-bis(2-phenol) groups as side-arms, is reported. The basicity behavior and the binding properties of L toward alkali metal ions were determined by means of potentiometric measurements in ethanol/water 50:50 (v/v) solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). The anionic H(-1)L(-) species can be obtained in strong alkaline solution, indicating that not all of the acidic protons of L can be removed under the experimental conditions used. This species behaves as a tetraprotic base (log K(1)=11.22, log K(2)=9.45, log K(3)=7.07, log K(4)=5.08), and binds alkali metal ions to form neutral [MH(-1)L] complexes with the following stability constants: log K(Li)=3.92, log K(Na)=3.54, log K(K)=3.29, log K(Cs)=3.53. The arrangement of the acidic protons in the H(-1)L(-) species depends on the polarity of the solvents used, and at least one proton switches from the amine moiety to the aromatic part upon decreasing the polarity of the solvent. In this way two different binding areas, modulated by the polarity of solvents, are possible in L. One area is preferred by alkali metal ions in polar solvents, the second one is preferred in solvents with low polarity. Thus, the metal ion can switch from one location to the other in the ligand, modulated by the polarity of the environment. A strong hydrogen-bonding network should preorganize the ligand for coordination, as confirmed by MD simulations. The crystal structure of the [Na(H(-1)L)].CH(3)CN complex (space group P2(1)/c, a=12.805(1), b=20.205(3), c=14.170(2) A, beta=100.77(1) degrees, V=3601.6(8) A(3), Z=4, R=0.0430, wR2=0.1181), obtained using CH(2)Cl(2)/CH(3)CN as mixed solvent, supports this last aspect and shows one of the proposed binding areas.     

Extrapolation of molar equilibrium constants to zero ionic strength and parameters dependent on it. Copper(II), nickel(II), hydrogen(I) complexes with glycinate ion and calcium(II), hydrogen(I) complexes with nitrilotriacetate ion

The stability constants of the complexes of glycinate ion with copper(II), nickel(II) and hydrogen(I) and of nitrilotriacetate ion with calcium(II) and hydrogen(I) and the ionic product of water (K(w)) were determined potentiometrically. The measurements were carried out at 25.0 degrees C in four different ionic strengths up to I (= I(c)) = 2.50 and two different ionic media (KNO(3) and (CH(3))(4)NNO(3)). Extrapolation of equilibrium constants to zero ionic strength and ionic strength corrections to equilibrium constants were carried out with the data obtained from both media using the TEC (thermodynamic equilibrium constant) equation and computer program. The constants of the potassium complexes with nitrilotriacetic acid at low ionic strength are also given. Successful attempts to predict equilibrium constants for other ionic media using TEC parameters and the procedure of the specific ion-interaction theory (SIT) are given. The variations of equilibrium constants with the ionic strengths and ionic media are demonstrated.     

Cation-cation interactions between NpO2(+) and UO2(2+) at different temperatures and ionic strengths

Cation-cation interactions between NpO(2)(+) and UO(2)(2+) were studied at different temperatures (283.15 K to 358.15 K) and different ionic strengths (3-4.5 mol dm(-3)) by spectrophotometry and microcalorimetry. The cation-cation complex between NpO(2)(+) and UO(2)(2+) was weak and became stronger as the temperature was increased from 283.15 K to 358.15 K. The molar enthalpy of complexation was directly determined for the first time by microcalorimetry to be (4.2 ± 1.6) kJ mol(-1) at 298.15 K, in good agreement with the trend in the stability constant at different temperatures. The small and positive enthalpy and entropy of complexation support the argument that the cation-cation complex between NpO(2)(+) and UO(2)(2+) is of inner-sphere type. At each temperature, the stability constants of the cation-cation complex were found to increase as the ionic strength was increased. The specific ion interaction theory (SIT) was used to obtain the stability constants at infinite dilution and variable temperatures.     

Unexpected dependence of the protonation constant of 2,2'-bipyridyl on ionic strength

The protonation constants of 2,2'-bipyridyl and ammonia have been determined by pH titration at 25 degrees , at ionic strengths of 0.1, 0.2, 0.5, 1.0, 1.5 and 2.0M obtained by using LiNO(3), NaNO(3), KNO(3), LiClO(4) and NaClO(4) as background electrolytes. The protonation constants generally change by about 0.3-0.4 log units for both ligands in nitrate media. A similar change in the protonation constant of ammonia was observed in perchlorate media. There is, however, a change of about 0.8-0.9 log units in the protonation constant of bipyridyl in the perchlorate media. This phenomenon is interpreted by postulating ion-pair formation between perchlorate and the protonated form of bipyridyl, HBp(+) + ClO(4)(-) rlharr2; HBp(+).ClO(4)(-) with formation constants of 0.54 in 2M lithium nitrate and 0.45 in 2M sodium nitrate.     

The acidic constants of 2-hydroxybenzohydroxamic acid in NaClO4 solutions at 25 degrees C

The protolysis equilibria of 2-hydroxybenzohydroxamic acid, H2SAX, have been studied at 25 degrees C in different ionic media by potentiometric titration with a glass electrode. The media were 0.513, 1.05, 2.21 and 3.5 mol/kg NaClO4. The constants beta(-p)(H2SAX<==>H(2-p)SAX(-p)+pH+), combined with salting effects of NaClO4 on H2SAX deduced from solubility determinations, were processed by the specific interaction theory, SIT, to give equilibrium constants at infinite dilution, log beta(-1)(o) = -7.655 +/- 0.013 and log beta(-2)(o) = -17.94 +/- 0.04, as well as specific interaction coefficients b(HSAX-,Na+) = 0.12 +/- 0.01 and b(SAX2-,Na+) = 0.17 +/- 0.02, molal(-1).     

Formation of Metallo-6(A)-((2-(bis(2-aminoethyl)amino)ethyl)amino)-6(A)-deoxy-beta-cyclodextrins and Their Complexation of Tryptophan in Aqueous Solution

A pH titration study shows that 6(A)-((2-(bis(2-aminoethyl)amino)ethyl)amino)-6(A)-deoxy-beta-cyclodextrin (betaCDtren) forms binary metallocyclodextrins, [M(betaCDtren)](2+), for which log(K/dm(3) mol(-)(1)) = 11.65 +/- 0.06, 17.29 +/- 0.05, and 12.25 +/- 0.03, respectively, when M(2+) = Ni(2+), Cu(2+), and Zn(2+), where K is the stability constant in aqueous solution at 298.2 K and I = 0.10 mol dm(-)(3) (NaClO(4)). The ternary metallocyclodextrins [M(betaCDtren)Trp](+), where Trp(-) is the tryptophan anion, are characterized by log(K/dm(3) mol(-)(1)) = 8.2 +/- 0.2 and 8.1 +/- 0.2, 9.5 +/- 0.3 and 9.4 +/- 0.2, and 8.1 +/- 0.1 and 8.3 +/- 0.1, respectively, where the first and second values represent the stepwise stability constants for the complexation of (R)- and (S)-Trp(-), respectively, when M(2+) = Ni(2+), Cu(2+), and Zn(2+). From comparisons of stabilities and UV-visible spectra, the binary and ternary metallocyclodextrins appear to be six-coordinate when M(2+) = Ni(2+) and Zn(2+) and five-coordinate when M(2+) = Cu(2+). The factors affecting the stoichiometries and stabilities of the metallocyclodextrins, are discussed and comparisons are made with related systems.     

The removal efficiency of chestnut shells for selected pesticides from aqueous solutions

The removal of selected pesticides such as carbofuran (CF) and methyl parathion (MP) using low-cost abundant sorbent chestnut shells from aqueous solutions has been investigated in the present study. The sorption parameters, i.e., contact time, pH, initial pesticide solution concentration and temperature have been studied. Maximum percent sorption (99+/-1%) was achieved for (0.38-3.80) x10(-4) and (0.45-4.5) x10(-4) mol dm(-3) of MP and CF pesticide solutions respectively, using 0.4 g of sorbent in 100 ml of solution for 30 min agitation time at pH 6. The Freundlich, Langmuir and Dubinin-Radushkevich (D-R) models have been applied, and their constants for methyl parathion and carbofuran, sorption intensity 1/n (0.55+/-0.02 and 0.54+/-0.04), multilayer sorption capacity C(m) (28.3+/-0.5 and 16.4+/-0.7) x10(-3) mol l(1-1/n)dm(3/n)g(-1), monolayer sorption capacity Q (22.5+/-0.5 and 10.8+/-0.3) x10(-6) mo lg(-1), binding energy, b (2.9+/-0.2 and 5.2+/-0.5) x10(4) dm(3)mol(-1), and sorption energy E (11.2+/-0.1 and 11.5+/-0.2 kJ mol(-1)) have been evaluated respectively. Lagergren, Morris-Weber and Reichenberg equations were employed to study kinetics of sorption process. Thermodynamic parameters DeltaH (-5.09+/-0.1 and 22.8+/-0.4 kJ mol(-1)), DeltaS (-4.33+/-0.0003 and 0.09+/-0.001 kJ mol(-1)K(-1)) and DeltaG((303K)) (-2.9 and -3.8 kJ mol(-1)) have been calculated for methyl parathion and carbofuran, respectively. The developed sorption procedure has been employed to environmental samples.