The thermodynamic model of inorganic arsenic species in aqueous solutions Potentiometric study of the hydrolitic equilibrium of arsenic acid

Protonation constants of arsenic acid were determined at different ionic strengths in NaClO(4) (0.1, 0.5, 1.0, 3.0 mol dm(-3)), NaCl (0.5 and 1.0 mol dm(-3)) and KCl (0.5, 1.0 and 3.0 mol dm(-3)) ionic media by means of a potentiometric study. The distribution of arsenate species was defined depending on two important variables in natural environments: pH and composition. All the experimentation was performed at 25 degrees C. The differences found in the protonation constants for different medium compositions, were explained by the different behaviour of the interaction parameters of the species considered in the different media and ionic strengths. These parameters were reported for all hydrolitic As(V) species and were calculated using the Modified Bromley's Methodology (MBM). The corresponding thermodynamic stepwise formation constants were also determined (log degrees K(1)=11.58+/-0.01, log degrees K(2)=7.06+/-0.01, log degrees K(3)=2.25+/-0.01). All the results obtained showed not only the importance of the ionic strength but also of the composition of the ionic medium on the distribution of the acid-base species of As(V) as a function of pH in natural waters.     

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.     

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   

Thermodynamic protonation constants of vardenafil by the nonlinear regression of multiwavelength pH-spectrophotometric titration data

pH-spectrophotometric titration data were used to determine protonation constants of vardenafil at different ionic strengths I and temperatures of 25°C and 37°C. The use of two different multiwavelength and the multivariate treatment of spectral data, SPECFIT32 and SQUAD(84) nonlinear regression analyses and INDICES factor analysis is presented. The reliability of the protonation constants of the drug was proven with goodness-of-fit tests of the pH-spectra. The thermodynamic protonation constants log K _T ⁱ were estimated by a nonlinear regression of (log K, I) data using the Debye-Hückel equation, yielding log K ₄ ^T = 3.59(1) and 3.26(1), log K ₃ ^T = 5.64(1) and 5.81(1), log K ₂ ^T = 9.41(1) and 8.59(2), log K ₁ ^T = 10.92(2) and 10.05(1) at 25°C and 37°C, where the figure in brackets is the standard deviation in last significant digit. Concurrently, the experimental determination of four thermodynamic protonation constants was combined with the computational prediction of the MARVIN program based on knowledge of the chemical structures of the drug and was in good agreement with its experimental value. The factor analysis of spectra in the INDICES program predicts the correct number of light-absorbing components when the instrument error is known and when the signal-to-error ratio SER is higher than 10.      

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.     

Evaluation of the Hydrophilic Property of Sodium Ion-pair Complexes with 3m-Crown-m Ethers (m = 5, 6) and Their Benzo-derivatives by Solvent Extraction

The ion-pair formation constants {K(j)(0): j = MA (metal salt), MLA} of NaO(2)CCF(3) (Na(+)tfa(-)) and its ion-pair complexes (MLA) in water (w) were determined potentiometrically at 25 degrees C and an ionic strength (I) of zero. 15-Crown-5 (15C5), 18-crown-6 ethers (18C6), and their mono-benzo derivatives were used as crown ethers (L). The extraction of Natfa by these four L from w into 1,2-dichloroethane was done at 25 degrees C, and then the extraction constants (K(ex)) for NaLtfa were calculated by using the K(j) values, which were estimated from the corresponding K(j)(0) ones at I of the w-phases, and other equilibrium constants. Also, the distribution constants (K(D,MLA)) of NaLtfa between the two phases were obtained from a thermodynamic cycle expressing K(ex). An interaction of w-molecules with NaLA was considered using a relation of log K(D,MLA) with log K(D,L), derived from the Scatchard-Hildebrand equation, where K(D,L) denotes the distribution constant of L between the two phases. The interaction increased in the order of NaL (picrate) < free L 相似文献   

Dioxouranium(VI)-carboxylate complexes. Speciation of UO2(2+)-1,2,3-propanetricarboxylate system in NaCl(aq) at different ionic strengths and at t=25 degrees C

The formation constants of dioxouranium(VI)-1,2,3-propanetricarboxylate [tricarballylate (3-), TCA] complexes were determined in NaCl aqueous solutions at 0 < or = I/mol L(-1) < or = 1.0 and t=25 degrees C, by potentiometry, ISE-[H+] glass electrode. The speciation model obtained at each ionic strength includes the following species: ML-, MLH0, ML2(4-) and ML2H3- (M = UO2(2+) and L = TCA). The dependence on ionic strength of protonation constants of 1,2,3-propanetricarboxylate and of the metal-ligand complexes was modeled by the SIT (Specific ion Interaction Theory) approach and by the Pitzer equations. The formation constants at infinite dilution are [for the generic equilibrium p UO22+ + q (L3-) + r H+ = (UO2(2+))p(L)qHr(2p-3q+r); betapqr]: log beta110 = 6.222 +/- 0.030, log beta111 = 11.251 +/- 0.009, log beta121 = 7.75 +/- 0.02, log beta121 = 14.33 +/- 0.06. The sequestering ability of 1,2,3-propanetricarboxylate towards UO2(2+) was quantified by using a sigmoid Boltzman type equation.     

海水中二甲基硫亨利常数的测定

 推导了多次相平衡顶空气相色谱法测定海水中二甲基硫 (DMS)亨利常数 (K)的理论关系式 ,根据两次或多次气、液相平衡的关系式 ,只测定DMS在气相中的浓度就可测定亨利常数。实测 2 2℃时DMS在胶州湾海水中的亨利常数是 0 0 89,相对标准偏差为 5 5 0 %。亨利常数的对数与环境水体中NaCl的质量分数 [w(NaCl) ]之间的关系为 :logK =0 0 688·w(NaCl) - 1 3 5 68,相关系数为 0 997。亨利常数的对数与环境水体的绝对温度 (T)的倒数之间的相关方程为 :logK =- 15 4 4 8/T + 4 2 112 ,相关系数为 0 996。     

Rigid MIIL2Gd2III (M = Fe, Ru) complexes of a terpyridine-based heteroditopic chelate: a class of candidates for MRI contrast agents

Rigid chelates of high-molecular weight, [M(tpy-DTTA)2]6- (M = Fe, Ru), are obtained upon self-assembly around one M(II) ion of two terpyridine-based molecules substituted in the 4'-position with the polyaminocarboxylate diethylenetriamine-N,N,N',N'-tetraacetate, tpy-DTTA4-. The protonation constants of tpy-DTTA4- (log K1 = 8.65(4), log K2 = 7.63(4), log K3 = 5.25(6), log K4 = 3.30(7)) and [Fe(tpy-DTTA)2]6- (log K1 = 8.40(4), log K2 = 7.26(4)) have been determined by potentiometry, 1H NMR and UV-vis titrations. The thermodynamic stability constant log K(GdL) of [Fe(tpy-DTTA)2Gd2(H2O)4] measured at 25 degrees C by potentiometry is 10.87. This relatively low value is due to the direct linkage of the polyaminocarboxylate part to the electron-withdrawing terpyridine. UV-vis absorbance spectra of [M(tpy-DTTA)2Gd2(H2O)4] and 1H NMR spectra of [M(tpy-DTTA)2Eu2(H2O)4] revealed similar solution behavior of the Fe and Ru complexes. An I(d) water-exchange mechanism (DeltaV++ = +6.8 +/- 1 cm3 mol(-1)) with a rate constant of k(ex)298 = (5.1 +/- 0.3) x 10(6) s(-1) has been found for [Fe(tpy-DTTA)2Gd2(H2O)4] by 17O NMR. A slow rotational correlation time (tau(RO) = 410 +/- 10 ps) and the presence of two water molecules (q = 2) in the coordination inner-sphere of each Gd(III) ion have also been determined for this complex. A remarkably high relaxivity has been observed for both [M(tpy-DTTA)2Gd2(H2O)4] complexes (at 20 MHz and 37 degrees C, r(1) = 15.7 mM(-1) s(-1) for the Fe complex, and r(1) = 15.6 mM(-1) s(-1) for the Ru complex).     

Equilibrium and formation/dissociation kinetics of some Ln(III)PCTA complexes

The protonation constants () of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine-containing macrocycle and several different metal ions have been determined in 1.0 M KCl at 25 degrees C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously, and a total of five protonation steps were detected (log = 11.36, 7.35, 3.83, 2.12, and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+, and Zn2+ were also somewhat higher than those previously reported, but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the Ln series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA) were followed by conventional UV-vis spectroscopy in the pH range 3.5-4.4. First-order rate constants (saturation kinetics) obtained for different ligand-to-metal ion ratios were consistent with the rapid formation of a diprotonated intermediate, Ln(H(2)PCTA)(2+). The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97, and 2.69 log K units for Ce(H(2)PCTA), Eu(H(2)PCTA), Y(H(2)PCTA), and Yb(H(2)PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate-determining step, and the rate constant (k(r)) for this process was found to be inversely proportional to the proton concentration. The formation rates (k(OH)) increased with a decrease in the lanthanide ion size [9.68 x 10(7), 1.74 x 10(8), 1.13 x 10(8), and 1.11 x 10(9) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively]. These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid-catalyzed dissociation rates (k1) varied with the cation from 9.61 x 10(-4), 5.08 x 10(-4), 1.07 x 10(-3), and 2.80 x 10(-4) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively.     

Taurocholate and taurodeoxycholate: gel formation and protonation constants

Taurocholate (TC) and taurodeoxycholate (TDC) in aqueous solutions, in the presence of sodium and hydrogen ions can give micellar products, even differently protonated. This phenomenon is investigated in this paper to explain whether the assumption of hydrogen ions is to attribute to the micellar aggregates, or to the protonation of taurocholate and taurodeoxycholate, respectively. In the course of this research, often the formation of gel occurred immediately after the mixture of the reagents (sodium, hydrogen ions and anions of bile acids) or after some time, depending on the concentrations of the reagents. No author mentions this evidence, but experiments carried out in the presence of gel are not reproducible because the investigated solutions cannot be considered in real equilibrium. The protonation study was performed by means of electromotive force measurements of a galvanic cell involving a glass electrode, at 25 degrees C and 1.00 mol dm(-3) NaCl, as ionic medium. The obtained protonation constants had the following values: log k1 = 0.07+/- 0.02 for TC and log k'1 = 1.60 +/- 0.03 for TDC.     

Analysis of variance applied to determinations of equilibrium constants

The statistical analysis of variance has been applied to the values of the equilibrium constants of the glycinate-proton and glycinate-nickel systems, determined in different laboratories by pH-titration in aqueous solution. The analysis shows how the main part of the error derives from the variability from one titration to another even in the same laboratory. Therefore the data for a single titration (k) must be processed separately, thus yielding a mean value for the equilibrium constant logbeta (pqr)(k) of the species M(p)H(q)L(r); from these mean values for different titrations in each laboratory l, a within-laboratory grand average, logbeta (pqr)(l), can be calculated; the variance of this grand average measures the experimental error. A further analysis of the data from the different participating laboratories shows that there were no significant differences between laboratories for the constants reported. From these results it can be inferred that all the values of the mean constants logbeta (pqr)(k) for one species, as determined separately for each titration in four laboratories, belong to the same population. A chi(2) analysis of these populations demonstrates that the stability constants of the species HL, H(2)L(+), NiL(+), NiL(2) (with L(-) = glycinate) are normally distributed, but not that for NiL(-)(3). Therefore, general mean values of the first four constants can be calculated and proposed as reliable standard values at 25 degrees and I = 1.0M Na(Cl): protonation of glycinate, log beta(011) = 9.651(12), log beta(021) = 12.071(26); nickel-glycinate complexes, log beta(101) = 5.615(35), log beta(102) = 10.363(62). These values indicate that the standard deviations are rather higher than those often reported in the literature.     

Protonation and complex formation of 5-sulfosalicylate in NaCl,CaCl2 and MgCl2 aqueous media. Speciation in synthetic seawater

The binding capacity of 5-sulfosalicylic acid (ssa) towards cationic macro-components of natural waters has been investigated in different ionic media (NaCl, MgCl2 and CaCl2 aqueous solutions) and in the ionic strength range 0 < or = I < or = 1 mol dm-3. In order to contribute to the speciation of this multi-sites ligand, measurements have been carried out also in a synthetic seawater (SSWE) containing the major components of seawater (Na+, K+, Ca2+, Mg2+, Cl- and SO4(2-)). Measurements have been performed by potentiometry ([H+]-glass electrode), at t = 25 degrees C. A critical analysis on the experimental and literature data is also given.     

Salt effects on the protonation and on alkali and alkaline earth metal complex formation of 1,2,3-propanetricarboxylate in aqueous solution

The protonation of 1,2,3-propanetricarboxylate (tricarballylate, tca) was studied in LiCl, NaCl, KCl, MgCl(2), CaCl(2) and tetraethylammonium iodide (Et(4)NI) aqueous solutions, at 25 degrees C, in the ionic strength range 0 < I < 1M, using the pH-metric technique. The differences between protonation constants determined in Et(4)NI and those determined in the other background salts were interpreted in terms of complex formations. Least squares calculations are consistent with the formation of MLH(j) (j = 0,1.2), M(2)LH(i) (i = 0,1,2), M(2)L species, when M = Mg(2+), Ca(2+). Potentiometric measurements performed in mixed NaClKCl, NaClCaCl(2) and MgCl(2)CaCl(2) solutions showed the formation of mixed metal complexes NaKL, NaKHL, NaCaL and CaMgL. The dependence on ionic strength of protonation and complex formation constants was evaluated using a simple Debye-Hückel type equation.     

Spectrophotometric determination of the first protonation constant of orthovanadate

The first protonation constant for VO(3-)(4) has been determined spectrophotometrically at 25 degrees in 1M sodium chloride and found to have the value log K = 13.29 +/- 0.01. Individual absorption spectra for VO(3-)(4) and HVO(2-)(4) have been calculated (for the range 218-350 nm) from experimental absorbance measurements.     

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 amide oxygen donor. Metal ion coordinating properties of the ligand nitrilotriacetamide. A thermodynamic and crystallographic study

The metal ion coordinating properties of ntam (nitrilotriacetamide) are reported. The protonation constant (pK) for ntam is 2.6 in 0.1 M NaClO(4) at 25 degrees C. Formation constants (log K(1)) in 0.1 M NaClO(4) at 25 degrees C, determined by (1)H NMR and UV-Vis spectroscopy are: Ca(II), 1.28; Mg(II), 0.4; La(III), 2.30; Pb(II), 3.69; Cd(II), 3.78; Ni(II), 2.38; Cu(II), 3.16. The measured log K(1) values for the ntam complexes are discussed in terms of the low basicity of the N-donor, as evidenced by the pK, and the effect of metal ion size on complex stability. The amide O-donors of ntam lead to the stabilization of complexes of large metal ions (Pb(II), Cd(II), La(III), Ca(II)) relative to log K1 for the NH3 complexes, while for small metal ions (Ni(II), Cu(II)) the amide O-donors lead to destabilization. This is discussed in terms of the role of chelate ring size in controlling metal ion size-based selectivity. The structures of [Pb(ntam)(NO3)2]2 (1) and [Ca2(ntam)3(H2O)2](ClO4)4.3H2O (2) are reported. For 1: triclinic, space group P1, a = 7.4411(16), b = 9.0455(19), c = 11.625(3) A, alpha = 69.976(4), beta = 79.591(4), gamma = 67.045(3) degrees, Z = 2, R = 0.0275. For 2: monoclinic, space group P2(1)/c, a = 10.485(2), b = 11.414(2), c = 38.059(8) A, beta = 92.05(3) degrees, Z = 4, R = 0.0634. Structure 1 is dimeric with two Pb atoms linked by bridging O-donors from the two ntam ligands. The coordination sphere consists of one N-donor and 3 O-donors from the ntam ligand, two O-donors from nitrates, and one bridging O-donor. The variation in bond length suggests a stereochemically active lone pair of electrons on the Pb. Structure 2 consists of two Ca(II) ions held together by 3 bridging O-donors from ntam groups. One Ca is 9-coordinate with two ntam ligands present, plus one bridging O-donor from the other Ca(II) ntam complex. The other Ca is 8-coordinate, with a single coordinated ntam, plus two coordinated H2O molecules, and two bridging O-donors from the other half of the complex. The role of M-O=C bond angles in controlling selectivity for metal ions on the basis of their size is discussed.     

Ionic strength dependence of formation constant-XVI. Protonation of some nitrophenols and dihydroxybenzoic acids in aqueous (tetraethylammonium iodide) solution at 25 degrees

The protonation of 2- and 3-nitrophenol (NO(2) Ph) and 2,X and 3,Y dihydroxybenzoic acids (DBA, X = 4,5,6; Y = 4,5) has been studied potentiometrically in aqueous tetraethylammonium iodide solutions, at T = 25 degrees in the ionic strength range 0.05:5 相似文献   

On the complex formation equilibria between iron (III) and sulfate ions

The equilibria have been investigated at 25 degrees C in 3 M NaClO4 using potentiometry, glass and redox Fe3+/Fe2+ half-cells, and UV optical absorptiometry. The concentration of the reagents was chosen in the intervals: 10(-4) < or = [Fe(III)] < or = 5.10(-3) M, 0.01 < or = [SO4(2-)]tot < or = 0.65 M. The value of [H+] was kept at 0.1 M or more to reduce the hydrolysis of the Fe3+ ion to less than 1%. Auxiliary constants, corresponding to the formation of Fe(II)-sulfate complexes and to the association of H+ with SO4(2-) ions, were taken from previous determinations. The experimental data could be explained with the equilibria [formula: see text] Equilibrium constants at infinite dilution, log beta 101 degrees = 3.82 +/- 0.17, log beta 102 degrees = 5.75 +/- 0.17 and log beta 111 degrees = 3.68 +/- 0.35, have been evaluated by applying the specific interaction theory.