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Rigid derivatives of the acyclic ligand PDTA4− (H4PDTA = propylenediamine-N,N,N′,N′-tetraacetic acid) were prepared by functionalization of a 1,3-diaminocyclobutyl spacer. The new ligands contain either four acetate groups attached to the central scaffold (H4L1) or incorporate pyridyl (H2L2) or propylamide (H2L3) units replacing two of the carboxylate groups. The ligand protonation constants and the stability constants of their Mn2+ complexes were determined using potentiometric and spectrophotometric titrations. The stability of the [Mn(L1)]2− complex was found to be significantly higher than that of the flexible [Mn(PDTA)]2− derivative (log KMnL = 10.78 and 10.01, respectively). A detailed study of the 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O NMR measurements evidence that the [Mn(L1)]2− and [Mn(L2)] complexes display a hydration equilibrium in solution involving a seven-coordinate species with an inner-sphere water molecule and a six-coordinate species that lacks a coordinated water molecule. As a result the 1H relaxivities of these complexes are somewhat lower than that of [Mn(EDTA)]2− and related systems. The introduction of propylamide groups in [Mn(L3)] shifts the hydration equilibrium to the seven-coordinate species, which results in a 1H relaxivity (r1p = 3.7 mM−1 s−1 at 22 MHz and 25 °C) exceeding that of [Mn(EDTA)]2− (r1p = 3.3 mM−1 s−1 at 22 MHz and 25 °C). The parameters that control the relaxivities in this family of complexes were determined by simultaneous fitting of the experimental 1H NMRD and 17O NMR data (transverse relaxation rates and chemical shifts), with the aid of computational studies performed at the DFT and CASSCF/NEVPT2 levels. These studies provide detailed insight of the parameters that control the efficiency of these relaxation agents at the molecular level.

We present two ligands containing a N-ethyl-4-(trifluoromethyl)benzenesulfonamide group attached to either a 6,6'-(azanediylbis(methylene))dipicolinic acid unit (H3DPASAm) or a 2,2'-(1,4,7-triazonane-1,4-diyl)diacetic acid macrocyclic platform (H3NO2ASAm). These ligands were designed to provide a pH-dependent relaxivity response upon complexation with Mn2+ in aqueous solution. The protonation constants of the ligands and the stability constants of the Mn2+ complexes were determined using potentiometric titrations complemented by spectrophotometric experiments. The deprotonations of the sulfonamide groups of the ligands are characterized by protonation constants of log KiH = 10.36 and 10.59 for DPASAm3- and HNO2ASAm2-, respectively. These values decrease dramatically to log KiH = 6.43 and 5.42 in the presence of Mn2+, because of the coordination of the negatively charged sulfonamide groups to the metal ion. The higher log KiH value in [Mn(DPASAm)]- is related to the formation of a seven-coordinate complex, while the metal ion in [Mn(NO2ASAm)]- is six-coordinated. The X-ray crystal structure of Na[Mn(DPASAm)(H2O)]·2H2O confirms the formation of a seven-coordinate complex, where the coordination environment is fulfilled by the donor atoms of the two picolinate groups, the amine N atom, the N atom of the sulfonamide group, and a coordinated water molecule. The lower conditional stability of the [Mn(NO2ASAm)]- complex and the lower protonation constant of the sulfonamide group results in complex dissociation at relatively high pH (

Rigid derivatives of the acyclic ligand PDTA4- (H

The nature of the axial ligand coordinated to the Yb3+ ion in [Yb(DOTAM)]3+ has profound consequences in the magnetic anisotropy and optical properties of the complex, as evidenced by 1H NMR and UV-vis spectroscopies. The pseudocontact shifts of 1H nuclei and the 2F5/2 ← 2F7/2 absorption band were found to be very sensitive to the nature of the axial ligand (MeOH, H2O, MeOH, or F-). The energy levels of the 2F5/2 and 2F7/2 manifolds in [Yb(DOTAM)(X)]3+ (X = MeOH, H2O, or dimethyl sulfoxide (DMSO)) and [Yb(DOTAM)F]2+ complexes were assigned from the analysis of the optical spectra and ab initio calculations based on CASSCF wave functions that considered dynamic correlation through perturbation theory (NEVPT2) and spin-orbit coupling effects. The magnetic anisotropies obtained with ab initio calculations are in good agreement with the experimental values derived from 1H NMR spectral data, though for the [Yb(DOTAM)(H2O)]3+ and [Yb(DOTAM)F]2+ complexes, the explicit inclusion of a few second-sphere water molecules is required to improve the calculated data. Crystal-field calculations show that the observed pseudocontact shifts do not correlate well with the crystal-field parameter B20, as predicted by Bleaney's theory. The change in the sign of the magnetic anisotropy from prolate (X = MeOH, H2O, or DMSO) to oblate in [Yb(DOTAM)F]2+ is related to the relative energies of the 4fz3 orbital and the 4fx3/4fy3 pair, which are affected by the coordination ability of the axial ligand.

We present two ligands containing a

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(III) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(III) ions thanks to μ2–η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(III) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(III) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(III) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (e = 8770 M−1 cm−1) that was attributed to the Bi(III)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl−, Br−, I− and N3−, respectively.

International audience; The heptadentate ligand L was shown to form extremely stable Gd complex at neutral pH with a pGd value of 18.4 at pH 7.4. The X-ray crystal structures of the complexes formed with Gd and Tb displayed two very different coordination behaviors being respectively octa-and nonacoordinated. The relaxometric properties of the Gd complex were studied by field dependent relaxivity measurements at various temperatures and by 17 O NMR spectroscopy. The pH dependence of the longitudinal relaxivity profile indicated large changes around neutral pH leading to a very large value of 10.1 mM-1. s-1 (60 MHz, 298 K) at pH 4.7. The changes were attributed to an increase of the hydration number from one water molecule in basic conditions to two at acidic pH. A similar trend was observed for the luminescence of the Eu complex, confirming the change in hydration state. DOSY experiments were performed on the Lu analogue, pointing to the absence of dimers in solution in the considered pH range. A breathing mode of the complex was postulated, further supported by 1 H and 31 P-NMR spectroscopy of the Yb complex at varying pH and was finally modeled by DFT calculations.

Reinforced cross-bridged Ni2+-cyclam complexes were functionalised with pendant arms containing both amide protons and CF3 groups that lead to a dual 1H/19F response. The resulting complexes possess very high inertness favourable for MRI applications. The paramagnetism of the Ni2+ ion shifts the amide resonance 56 ppm away from bulk water favouring the chemical exchange saturation transfer (CEST) effect and shortening the acquisition times in 19F magnetic resonance imaging (MRI) experiments, thus enhancing the signal-to-noise ratios compared to the fluorinated diamagnetic reference.

Reinforced cross-bridged Ni2+-cyclam complexes were functionalised with pendant arms containing both amide protons and CF3 groups that lead to a dual 1H/19F response. The resulting complexes possess very high inertness favourable for MRI applications. The paramagnetism of the Ni2+ ion shifts the amide resonance 56 ppm away from bulk water favouring the chemical exchange saturation transfer (CEST) effect and shortening the acquisition times in 19F magnetic resonance imaging (MRI) experiments, thus enhancing the signal-to-noise ratios compared to the fluorinated diamagnetic reference.

[Abstract] We report a pentadentate ligand containing a 2,2′-azanediyldiacetic acid moiety functionalized with a picolinate group at the nitrogen atom (H3paada), as well as a lipophylic derivative functionalized with a dodecyloxy group at position 4 of the pyridyl ring (H3C12Opaada). The protonation constants of the paada3− ligand and the stability constant of the Mn(II) complex were determined using a combination of potentiometric and spectrophotometric titrations (25 °C, 0.15 M NaCl). A detailed relaxometric characterisation was accomplished by recording 1H Nuclear Magnetic Relaxation Dispersion (NMRD) profiles and 17O chemical shifts and relaxation rates. These studies provide detailed information on the microscopic parameters that control their efficiency as relaxation agents in vitro. For the sake of completeness and to facilitate comparison, we also characterised the related [Mn(nta)]− complex (nta = nitrilotriacetate). Both the [Mn(paada)]− and [Mn(nta)]− complexes turned out to contain two inner-sphere water molecules in aqueous solution. The exchange rate of these coordinated water molecules was slower in [Mn(paada)]− (k298ex = 90 × 107 s−1) than in [Mn(nta)]− (k298ex = 280 × 107 s−1). The complexes were also characterised using both DFT (TPSSh/def2–TZVP) and ab initio CAS(5,5) calculations. The lipophylic [Mn(C12Opaada)]− complex forms micelles in solution characterised by a critical micellar concentration (cmc) of 0.31 ± 0.01 mM. This complex also forms a rather strong adduct with Bovine Serum Albumin (BSA) with an association constant of 5.5 × 104 M−1 at 25 °C. The enthalpy and entropy changes obtained for the formation of the adduct indicate that the binding event is driven by hydrophobic interactions. Authors R. P.-P., I. B., E. I., C. P.-I. and D. E.-G. thank Ministerio de Economía y Competitividad (CTQ2016-76756-P) and Xunta de Galicia (ED431B 2017/59 and ED431D 2017/01) for generous financial support and Centro de Supercomputación of Galicia (CESGA) for providing the computer facilities. R. P.-P. thanks Ministerio de Economía y Competitividad for a PhD FPI grant (BES-2014-068399) and a fellowship for a short term stay in Alessandria (EEBB-I-18-13075). R. U.-V. thanks Xunta de Galicia for a PhD grant (ED481A-2018/314). M.B. and F.C. are grateful to Università del Piemonte Orientale for financial support (Ricerca locale 2016). This work was carried out within the framework of the COST CA15209 Action “European Network on NMR Relaxometry” Xunta de Galicia; ED431B 2017/59 Xunta de Galicia; ED431D 2017/01 Xunta de Galicia; ED481A-2018/314

We report a detailed study of the structure of the [Bi(DO3A)] complex both in the solid state and in solution. The X-ray crystal structure of [Bi(DO3A)] evidences the octa-coordination of the Bi(iii) ion, which is directly coordinated to the four nitrogen atoms of the cyclen unit and three oxygen atoms of the carboxylate groups. The octa-coordination is completed by an oxygen atom of a neighboring carboxylate group, which bridges Bi(iii) ions thanks to μ2-η1:η1 coordination, resulting in the formation of a coordination polymer. The Bi(iii) ion presents a twisted-square antiprismatic (TSAP) coordination geometry associated with the Δ(δδδδ)/Λ(λλλλ) enantiomeric pair. A computational DFT study indicates that the 6s2 lone pair of Bi(iii) is stereochemically active in [Bi(DO3A)] and most of the cyclen-based complexes reported in the literature. Depending on the spatial arrangement of the donor atoms of the ligand the lone pair points in different directions, so that Bi(iii) can easily accommodate different coordination environments. In solution the [Bi(DO3A)] complex exists as a monomeric complex, as demonstrated by DOSY measurements. The stability constant of the [Bi(DO3A)] complex, determined by using batch spectrophotometric titrations, was found to be rather high (log K = 26.85(5)). The complex presents characteristic absorption in the UV spectrum at 299 nm (ε = 8770 M-1 cm-1) that was attributed to the Bi(iii)-centered 6p ← 6s band on the basis of TDDFT calculations. Spectrophotometric titrations reveal weak binding of different anions to the [Bi(DO3A)] complex, with association constants of K11 = 3.55(8), 3.09(7), 6.2(1) and 2.19(5) for Cl-, Br-, I- and N3-, respectively.

The Ni2+ complexes with hexadentate ligands containing two 6 methylpicolinamide groups linked by ethane-1,2 diamine (H2dedpam) or cyclohexane-1,2 diamine (H2chxdedpam) spacers were investigated as potential contrast agents in magnetic resonance imaging (MRI). The properties of the complexes were compared to those of the analogues containing 6 methylpicolinate units (dedpa2 and chxdedpa2 ). The X ray structure of the [Ni(H2dedpam)]2+ complex reveals a six-coordinated metal ion with a distorted octahedral environment. The protonation constants of the dedpa2 and H2dedpam ligands and the stability constants of their Ni2+ complexes were determined using pH-potentiometry and spectrophotometric titrations (25 ºC, 0.15 M NaCl). The [Ni(dedpa)] complex (logKNiL = 20.88(1)) was found to be considerably more stable than the corresponding amide derivative [Ni(H2dedpam)]2+ (logKNiL = 14.29(2)). However, the amide derivative [Ni(H2chxdedpam)]2+ was found to be considerably more inert with respect to proton-assisted dissociation than the carboxylate derivative [Ni(chxdedpa)]. A detailed 1H NMR and DFT study was conducted to assign the 1H NMR spectra of the [Ni(chxdedpa)] and [Ni(H2chxdedpam)]2+ complexes. The observed 1H NMR paramagnetic shifts were found to be dominated by the Fermi contact contribution. The amide resonances of [Ni(H2chxdedpam)]2+ at 91.5 and 22.2 ppm were found to provide sizeable chemical exchange staturation transfer effect, paving the way for the development of NiCEST agents based on these rigid non-macrocyclic platforms.

Differential pulse polarography (DPP) was used to study the complexation of cadmium by cysteine (CySH) at pH = 7.8 and l = 0.7 M (KNO3), as well as to determine the stability constants of the equilibria Cd2+ + CyS− ⇄ Cd(CyS)+ and Cd(CyS)+ + CyS− ⇄ Cd(CyS)2. Copyright © 1993 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim

The steady-state fluorescence emission from the local anaesthetic tetracaine (TCA) in water-solvent mixtures and in the presence of α-, β- and γ-cyclodextrin (CD) was investigated at various pH values. Emission was observed from the locally and the intramolecular charge transfer excited states. The TCA-CD system was found to be characterised by 1:1 associate in every case. The association constants of each complex were determined. Ministerio de Educación y Ciencia; CTQ2005-07428/BQU Ministerio de Ciencia e Innovación; CTQ2008-04429/BQU

Acid−base equilibrium constants for the two amino groups of the procaine molecule have been determined at 25 °C in different saline media (NaCl, KCl, and CaCl2), by means of potentiometric titrations. The Pitzer model has been used to deal with the ionic strength dependence of activity coefficients, and the parameters proposed by this theory have been obtained, including the thermodymanic dissociation constants, pKT. Equations describing the dependence of stoichiometric acid−base equilibrium constants versus ionic strength are given.

The UV-vis absorption and the fluorescence emission spectra of novocaine were analysed in aqueous cyclodextrin (CD) solutions. Either the absorbance read at λmax 290 nm or the fluorescence emission intensity at λems 346 nm increase in the presence of both α- and β-CD due to the formation of 1:1 inclusion complexes. The lower polarity of the CD-cavity sensed by the included drug enhances the emitted fluorescence; in fact, the same effect was observed in aqueous mixtures of acetonitrile, dioxane, or dimethylsulfoxide. The inclusion complex formation between the monocation of novocaine and CDs diminishes the electrical conductance of aqueous solutions of novocaine hydrochloride (NoHCl). Both the nitrosation reaction in aqueous acid medium and the ester hydrolysis in alkaline medium are retarded in the presence of CDs. The strongest effect was observed with β-CD as a consequence of the higher stability inclusion complex.

In aqueous solutions, the kinetic features of both the hydrolysis reaction of the ester function of novocaine in alkaline medium and the nitrosation reaction of the primary amine group of novocaine in mild acid medium were investigated by UV/vis spectroscopy. The ester hydrolysis shows first-order kinetics with respect to both the drug and the nucleophile, OH-, concentrations, thus following a typical S(N)2 (Ac) mechanism. The rate of the reaction decreases strongly with the polarity of the reaction media, analyzed for both dioxane-water and Me2SO-water mixtures. The effect of the presence of cationic micelles of tetradecyltrimethylammonium bromide, TTABr, was abnormal in that it inhibits the rate of the reaction throughout the analyzed concentration range of the surfactant. The same pattern of behavior is observed in the presence of anionic micelles of sodium dodecyl sulfate (SDS); however, the effect is more pronounced. The rate equation obtained in the kinetic study of the nitrosation reaction of novocaine in mild acid medium contains first- and second-order terms with respect to [nitrite], which correspond with the two parallel reaction paths due to nitrosation via both NO+ and N2O3, respectively; the rate of the reaction also increases with both the [H+] and the total acetic acid-acetate buffer concentration. In contrast to the ester hydrolysis, the nitrosation reaction is accelerated in aqueous micellar solutions of both cationic and anionic surfactants of TTABr and SDS, respectively.

Activity coefficient of triethanolamine (TEA) in major seawater salts (NaCl, KCl, CaCl2 and MgCl2) has been determinated using the distribution method. It increases slowly in KCl, remains almost constant in NaCl and decreases in the other salts. Pitzer model has been used to fit the experimental data and the corresponding interaction parameters have been determinated.

Several reported procedures for calibrating glass electrodes in proton concentration are compared. Some recommendations for non-experts are also given. The examined procedures can be classified into two broad categories, namely: those based on direct potential difference measurements of solutions of known proton concentration and those that use one or several pH standards to calibrate the electrode and subsequently measure the pH of solutions containing known proton concentrations. With a single buffer, the two types of procedures lead to equivalent results. However, if two pH buffers are used, the slope of the calibration graph in proton concentration will differ from the real electrode slope to an extent proportional to the difference between the liquid junction potentials of the two buffers. Therefore, any other method is preferable under these circumstances.

A kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol kg−1) were obtained, and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behavior at high ionic strength, when Debye–Huckel limiting law is no longer valid. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 650–660, 2004

The alkaline hydrolysis of two aromatic esters, 2-naphthyl acetate (2NA) and phenyl acetate (PhA) has been tackled in this work. The reaction has been followed in water and in the presence of cationic surfactants with different chain lengths: dodecyltrimethylammonium bromide (DTABr), tetradecyltrimethylammonium bromide (TTABr), and hexadecyltrimethylammonium bromide (CTABr) and the corresponding hydroxides (DTAOH, TTAOH and CTAOH) at 25. °C. The pseudo-first order rate constants increase with surfactant concentration in the presence of surfactants with reactive counter-ions, while a maximum is reached for bromide surfactants with a constant concentration of hydroxyl ion. Both, the association equilibrium constants of 2NA and PhA with micelles and the rate constant in this medium were determined. The degree of counter-ion association to micelles was considered as a variable parameter, using the adsorption equilibrium of bromide and hydroxide ions to the micelle. Ministerio de Educación y Ciencia; CTQ2005-07428/BQU Ministerio de Ciencia e Innovación; CTQ2008-04429/BQU

With the aim to surpass the concentration limit imposed by the Bates-Guggenheim convention, the Pitzer formalism has been applied to the analysis of the standardization of the pH buffer, potassium tetraoxalate dihydrate. Following the same procedure that has been conventionally applied to other pH buffers, hydrogen electrodes have been used to measure the potential differences of Harned cells, which contained 0.05 mol·kg-1 potassium tetraoxalate and up to 1 mol·kg-1 KCl, at 25 °C. A value of pH = 1.650 has been calculated. Another simpler model for activity coefficients, the Guggenheim specific interaction theory, has been found to be inadequate to model this complex system.

The protonation constants of acetic, chloroacetic, and phenylacetic acids in KNO3 at 25 °C at several ionic strengths were determined by potentiometry with a glass electrode. pK* versus I plots were fitted to Pitzer equations as well as reported pK* data. The most salient conclusion reached is that all acid−electrolyte interaction parameters show roughly the same value irrespective of the particular carboxylic acid. On the basis of this finding, an average equation that reproduces the behavior of simple carboxylic acids in different saline media was developed.

The complexation constants of neutral and protonated procaine (also called novocaine) with β-cyclodextrin have been obtained as a function of sodium chloride concentration, at 25 °C, using the pote...

We examined the variation with ionic strength ( I , adjusted with KCl, KNO 3 , KBr, NaCl or NaClO 4 ) of the formal potential ( E const ) for glass electrodes exhibiting a Nernstian response (i.e. E cell = E const − s log [H + ]). For this purpose, we investigated the different factors included in the formal potential, so we obtained reported values for the liquid junction potential as a function of ionic strength and determined the logarithm of the activity coefficient for the proton in various saline media, using Pitzer equations.

Ionization constants for benzoic, m-nitrobenzoic and o-chlorobenzoic acids are experimentally determined in aqueous KNO3 solutions and ionic strength dependence of data are analysed by using Guggenheim's model for activity coefficients. Moreover, for benzoic acid, energetic contributions ΔGex in the minimum of the pK–ionic strength curve are calculated. It is found that ca. 20% of the total excess energy is due to the non-Debye–Huckel term. A discussion of pK*(I) in terms of solvation energy is also given.

The dependence of the ionic strength of stoichiometric protonation constants, obtained potentiometrically, of several amino acids has been analysed by the mean spherical approximation (MSA), a mathematically simple statistical mechanical treatment based on integral equations. Unlike the Debye–Huckel equation, which overestimates the effects of ion–ion interactions as the sizes of all ions are neglected, the MSA represents the electrolytes as a mixture of hard spheres immersed in a dielectric continuum which represents the solvent. This approach fits experimental data using concentration, electrical charge and diameter concepts and is an alternative to semiempirical models based on different ionic strengths with coefficients that defy theoretical interpretation. Analysis of data using both semiempirical models and a quasi-lattice model, not containing Debye–Huckel terms, is also included.

The effect of the ionic strength on the second acid-base equilibrium constant of various aminoacids was analysed by use of a quasi-lattice model for log γ± over the ionic strength range 0.1 -1.5 M. Such treatment provides an alternative to empirical or semi-empirical equations based on modified versions of Debye-Huckel limiting law obtained by including different ionic strength terms. An interpretation of the minimum of the curve in terms of the model employed is also given. © by R. Oldenbourg Verlag, Munchen 1997.

The nitrosation of acetylacetone (AcAc) has been revised in an aqueous acid medium of perchloric acid and buffers of mono-, di-, or tri-chloroacetic acid. The results show that in the presence of buffers, under conditions of [nit] ≪ [AcAc] (nit = sodium nitrite) the reaction cannot be studied by UV-Vis spectroscopy, contrary to the recently published paper by García-Rio et al. (J. Org. Chem., 2008, 73, 8198). The present study also corroborates the previously published mechanism of AcAc nitrosation, where no base-catalysis was observed. Contrarily, the low effect of buffers was attributed to the formation of nitrosyl chloro-, dichloro- or trichloro-acetate salts that are new nitrosating agents. Ministerio de Ciencia e Innovación; CTQ2008-04429/BQU

In the present work we obtained the experimental pKs of the amino acid alpha-alanine in NaCl at 25 degrees and different ionic strengths. The equilibrium constants have been potentiometrically determined with a commercial glass electrode and the results analysed through three models: two directly based on the Pitzer and Scatchard approaches to the ion specific interaction theory and the other based on a simpler modification of the Debye-Huckel equation. The three models fit the data reasonably well and the extrapolated pK values obtained show a good agreement. The goodness of the ridge regression method cannot be probed in this case.

We studied the influence of ionic strength on the stoichiometric equilibrium ionization constant of water in KNO 3 at 25°C by applying the Pitzer equations to the activity coefficients for the species in equilibrium. Reported values for NaCl and KCl media are also analysed

The ionization constants of glycine in artificial seawater containing NaCl, KCl, CaCl2, MgCl2 and Na2SO4 were potentiometrically determined at 25 ° C by using a commercial glass electrode. Measurements were carried out at different salinities, and thus ionic strengths, to simulate seawater and estuarine waters. The experimental data were fitted using different equations as functions of the salinity based on Millero (1979). Comparisons were made between the parameters obtained by changing the variables and also the parameters yielded by the Pitzer interaction model, which was previously applied by Millero to seawater systems. After considering all the proposed models we found the function in S12 to give the best fit and the smallest standard deviation of the parameters, although the extrapolated pK is not as good as the one obtained by the use of Pitzer's model. Some of the models we used yielded extrapolated pKs closer to the values in the literature (2.36 and 9.78) but higher standard deviations in the parameters.

We have potentiometrically determined the protonation constants of glycine in NaCl solutions of variable ionic strength. The data thus obtained have been analysed by using the interaction models of Scatchard and Pitzer. The presence of multicollinearity among the explanatory variables of the model has been evidenced through the coefficients of the correlation matrix and the variance inflation factor (VIF). We have applied the ridge regression (RR) to address the problem arising' from multicollinearity and the results are critically compared with those obtained by ordinary least squares regression (OLS).

The bacterial fish pathogen Vibrio anguillarum serotype O2 strain RV22 produces the mono catecholate siderophore Vanchrobactin (Vb) under conditions of iron deficiency. Vb contains two potential bidentate coordination sites: catecholate and salicylate groups. The iron(iii) coordination properties of Vb is investigated in aqueous solutions using spectrophotometric and potentiometric methods. The stepwise equilibrium constants (logK) for successive addition of Vb dianion to a ferric ion are 19.9; 13.3, and 9.5, respectively, for an overall association constant of 42.7. Based on the previous results, we estimated the equilibrium concentration of free iron(iii) under physiological conditions for pH 7.4 solution containing 10-6 M total iron and 10-5 M total Vb as pFe = 20 (=-log[Fe3+]). The Vb model compounds catechol (Cat) and 2,4-dihydroxy-N-(2-hydroxyethyl)benzamide (Dhb) have also been examined, and the obtained results show that the interaction of the whole system of Vb that contains the ferric-chelating groups of both Dhb and Cat, is synergically greater than the separate parts; i.e. Vb is the best chelating agent either in acid or basic media. In summary, bacteria employing Vb-mediated iron transport thus are able to compete effectively for iron with other microorganisms within which they live. Ministerio de Educación y Ciencia; CTQ2008-04429 Ministerio de Educación y Ciencia; CTQ2005-00793 Galicia. Consellería de Economía e Industria; 10PXIB103157PR

The complexation of several local anaesthetics by β and γ-cyclodextrins was studied by potentiometry with glass electrode. Tetracaine and dibucaine complexation constants were determined at 25°C in the presence of 0.1 M of NaCl. It was found that prilocaine and lidocaine complexes cannot be detected. Ministerio de Educacion y Ciencia; CTQ2005-07428/BQU Ministerio de Ciencia e Innovacion; CTQ2008-04429/BQU

A systematic study of the dependence of acid-base stoichiometric constants on the ionic strength has been carried out for the aminoacidL-valine in ClK and BrK solutions. The observed dependence has been interpreted by using Guggenheim, Scatchard and Pitzer models for the activity coefficients of the species involved in the equilibria.

On the basis of the ionic strength dependence of the equilibrium constant (pK*) of thriethanolamine (TEA) and glycine, the ionic interaction parameters of the species involved in the equilibria TEAH+ ↔ TEA + H+ (for TEA), AH2+ ↔ AH + H+ and AH ↔ A- + H+ (for glycine) in aqueous solutions of KCl and KNO3, respectively, were determined using the Pitzer equations. Values of pK* were expressed on both the molarity and the molality scale at various temperatures and values of thermodynamic quantities ∆G0, ∆H0 and ∆S0 ascertained, for TEA.

In this work we carried out a simple mathematical analysis of the functions describing the dependence of the stoichiometric acid-base constant on application of Pitzer's formalism to the activity coefficients of the species involved in two common monoprotonation equilibria. Simulated pK* vs ionic strength plots for two typical acid-base equilibria AH+2 ⇆ AH + H+ and AH ⇆ A− + H+) are compared with experimental data for the two pK*i of β-alanine in KNO3 at 25 °C.

Nous avons determine les constantes stoechiometriques d'equilibre acide-base pour la L-valine dans des melanges equimolaires de KCl-KBr et KCl-KNO 3 et pour la triethanolamine dans des solutions de KCl-KBr. Ces determinations ont ete effectuees a des forces ioniques de 0.1 a 1.5. Les donnees ont ete analysees au moyen des equations de Pitzer et Guggenheim pour les coefficients d'activite des especes presentes

Acid–base equilibrium constants of triethanolamine (TEA) have been determined by potentiometric titrations with a glass electrode, at 25 °C. Ionic strength was kept constant with only one electrolyte (using one of these salts: NaCl, KCl, MgCl2 or CaCl2), with binary mixtures of MgCl2 and CaCl2, and finally, in a solution with a composition approximately similar to that of natural seawater without sulfate. Equilibrium constants have been expressed in function of ionic strength by means of Pitzer equations and interaction parameters proposed in this theory have been obtained. It has been found that acid–base behaviour of TEA depends greatly on the salt used: basicity of TEA is decreased by CaCl2, while it is increased by the other electrolytes used in this work.

In this paper we study the ionic strength dependence of the potentiometrically determined stoichiometric equilibrium constant (K*) of the amino acids a-alanine (CH3CHNH2COOH), leucine ((CH3)2CHCH2CHNH2-COOH), threonine (CH3CHOHCHNH2COOH), and methionine (CH3SCH2CH2CHNH2COOH) in artificial sea water at 25 °C and different ionic strengths. The results have been interpreted by the Pitzer interaction model. © 1995, American Chemical Society. All rights reserved.

In this paper, the stoichiometric acid-base equilibrium constants for the amino acids α-alanine, γ-aminobutyric acid, and ϵ-aminocaproic acid have been determined in KNO3 aqueous solutions at different ionic strengths and 25 °C. Experimental values of pKm,i app have been plotted as a function of the ionic strength by using the Guggenheim, Scatchard, and Pitzer models for the activity coefficients of the species present at equilibria. Results have been briefly discussed. © 1993, American Chemical Society. All rights reserved.

The renewed theoretical interest in the proton transfer associated to the amino group together with the scarcity of acid-base studies of amines in moderate to concentrated saline media focussed our attention on the study of the basicities of some alkylamines, namely monomethyl, dimethyl and trimethylamine, in aqueous saline solutions of KCl at various temperatures. A non-conventional analysis of stoichiometric equilibrium constants versus ionic strength data is carried out. On one hand, Pitzer’s model is easily applied to calculate the salting coefficient and the thermodynamic equilibrium constant of the alkylamines. On the other hand, the mean spherical approximation has the advantage over the Debye–Hückel based theories that it can account for effects produced by species of different sizes. Here, it is applied to predict the dependence of the salting behavior on the size of the alkylamines. Xunta de Galicia; XUGA 10310B97