Log Β2 Research Articles

Electrochemical Study of the Mixed Ligand Complexes of Co(II) and Ni(II) with Acetylsalicylic Acid and Nicotinamide

The interaction of acetylsalicylic acid (aspirin, aspH) and nicotinamide (NA) with Co(II) and Ni(II) ions was investigated using square-wave and cyclic voltammetry techniques. In the presence of Ni(II)/Co(II),nicotinamide gave new peaks at -0.85V and soh.12 V, corresponding to the reduction of Ni(II)-nicotinamide(log β1:2 =5.97) and Co(II)-nicotinamide (log β1:2 =5.19) complexes, respectively. In the presence of Ni(II)/Co(II), acetylsalicylic acid gave new peaks at -0.91V and -1.19 V, respectively, corresponding to the reductionof Ni(II)-salicylate (log β1:2 =8.48) and Co(II)-salicylate (log β1:2 =8.14) complexes. In the presence of nicotinamide, Ni(II)-salicylate and Co(II)-salicylate form mixed ligand complexes, reducing at -0.78V (log β1:2:2 =9.68) and -1.14V (log β1:2:2 =8.64), respectively.

Selective Extraction and Separation of Thorium from Monazite Using N-Phenylbenzo-18-crown-6-hydroxamic Acid

A method for the liquid–liquid extraction, separation, preconcentration and trace determination of thorium with N-phenylbenzo-18-crown-6-hydroxamic acid (PBCHA) is described. Thorium is extracted from the dichloromethane solution of PBCHA at pH 4.5 which gives a colourless extract (λmax 375 nm, e=1.5×104 L mol−1 cm−1, linear range following Beer’s law 0.77–18.48 µg mL−1). The extract is directly inserted into the plasma for ICP-AES measurements of thorium. A linear calibration graph was obtained between 10 and 130 ng mL−1 of thorium. The proposed method has been applied for the separation and determination of thorium in the presence of several ions in monazite sand, rare earths, sand and sea water samples. The thorium-PBCHA complexes are very stable, having the formation constant (log β2) 13.45 compared to lanthanum (log β2) 2.95, cerium (log β2) 2.95 and uranium (log β2) 3.80. Hence, thorium can easily be separated and determined in monazite sand.

Study of the Reaction of Platinum(IV) with Dimethylglyoxime by UV Spectrophotometry

The complex formation of dimethylglyoxime and platinum(IV) in alkaline medium has been investigated by ultraviolet spectroscopy. This study has shown that more than one complex species exists in solution. The effects of pH variation of ammonia buffer solution from 6.0 to 13.0 were investigated with respect to the absorption spectra. The molar ratios method, the Job's method and the method of relative recovery of complex species were used. It was found that the stoichiometric ratio Pt(IV)/dimethylglyoxime was 1:1, 1:2 and 2:1. The molar absorptivity (log ε = 4.1 at 260 nm) and the formation constant of the complex (log K2,1 = 15.0) were obtained. The stability constants of the [Pt(Hdmg)2(NH3)2] complex determined by the molar ratios and Job's method were log β2 = 9.2 ± 0.2 and log β2 = 9.3 ± 0.2, respectively.

Equilibria and dynamics of some aqueous peroxomolybdophosphate catalysts: a potentiometric and31P NMR spectroscopic study

The equilibrium speciation in the pH+ + qMoO42− + rH2O2 + sH2PO4− + tSO42− ⇌ (H+)p(MoO42−)q(H2O2)r(H2PO4−)s(SO42−)tp−2q−s−2t system in 0.300 M Na2(SO4) medium at 25 °C and [H2O2]tot/[Mo]tot > 2 has been determined from potentiometric data and 31P NMR integral and chemical shift data in the range 1.0 ≤ pH ≤ 9.0, 2.0 ≤ [MoO42−]tot/mM ≤ 293, 32 ≤ [H2O2]tot/mM ≤ 640, 2 ≤ [H2PO4−]tot/mM ≤ 60 and 200 ≤ [SO42−]tot/mM ≤ 380. Species with the following compositions were obtained: MoX2P3− (0,1,2,1,0), MoX2P2− (1,1,2,1,0), MoX2P− (2,1,2,1,0), Mo2X4P3− (2,2,4,1,0), Mo2X4P2− (3,2,4,1,0), Mo3X6P3− (4,3,6,1,0), Mo3X6P2− (5,3,6,1,0) and Mo4X8P3− (6,4,8,1,0). The numbers and charges of molybdenum (Mo), peroxide (X), phosphate (P) and sulfate (S) in each species are given in the abbreviated formula MoqXrPsStp−2q−s−2t. The numbers in parentheses refer to the values of p, q, r, s and t in the formula above. The following formation constants with 3σ were obtained; log β0,1,2,1,0 = 5.16 ± 0.09, log β1,1,2,1,0 = 12.73 ± 0.02 (pKa = 7.63), log β2,1,2,1,0 = 16.14 ± 0.03 (pKa = 3.42), log β2,2,4,1,0 = 25.03 (± 0.04), log β3,2,4,1,0 = 29.54 ± 0.02 (pKa = 4.51), log β4,3,6,1,0 = 42.30 ± 0.03, log β5,3,6,1,0 = 44.06 ± 0.08 (pKa = 1.76), log β6,4,8,1,0 = 57.30 ± 0.07. pKa values for H3PO4 and H2PO4− were determined to 2.00 and 6.48, respectively. Chemical exchange processes were detected by 31P NMR 2D EXSY and selective magnetisation transfer experiments between the complexes. An averaged lifetime, τ(X2Mo–OP) ∼ 30 ms, can be estimated for the MoX2P and Mo2X4P species at pH = 5.5 and 5 °C.

Reaction of Plutonium(VI) with Orthosilicic Acid Si(OH)4

Reaction of Pu(VI) with Si(OH)4 (at concentration 0.004–0.025 mol l–1) in a 0.2 M NaClO4 solution at pH 3–8 is studied by spectrophotometric method. In the range of pH 4.5–5.5, PuO2(H2O)4OSi(OH)3+ complex is formed, while at pH > 6, PuO2(H2O)3O2Si(OH)2 or hydroxosilicate complex PuO2(H2O)3(OH)OSi(OH)3 is recorded. The equilibrium constants are calculated for the reactions of formation of PuO2(H2O)4OSi(OH)3+ and PuO2(H2O)3O2Si(OH)2 and their concentration stability constants: log K1 = –3.91 ± 0.17 and log K2≈ –10.5; log β1= 5.90 ± 0.17 and log β2≈ 12.6. The PuO2(H2O)4OSi(OH)3+ complex is significantly less stable than analogous complex of U(VI). Calculations of the forms of Pu(VI) occurrence at the Si(OH)4 concentration equal to 0.002 mol l–1 showed that the maximum fraction of the PuO2(H2O)4OSi(OH)3+ complex is ∼10% (pH 6.5), while the fraction of PuO2(H2O)3O2Si(OH)2 is almost 40% (pH 8).

A speciation study of the aqueous H+/H2VO4–/H2O2/L-α-alanyl-L-serine system

A detailed study of the quaternary aqueous H+/H2VO4−/H2O2/L-α-alanyl-L-serine (Alaser) system has been performed at 25 °C in 0.150 M Na(Cl) medium, representing the ionic strength of human blood, using quantitative 51V NMR and potentiometric data (glass electrode). Data were evaluated with the computer program LAKE, which is able to treat combined EMF and NMR data. The pKa-values for Alaser were determined as 8.04 ± 0.01 and 3.07 ± 0.01. The errors given are 3σ. In the ternary H+/H2VO4−/Alaser system, two complexes, (H+)p(H2VO4−)q(Alaser)r, having (p, q, r) values (0, 1, 1) and (−1, 1, 1) with log β0,1,1 = 2.42 ± 0.01 and log β−1,1,1 = −5.80 ± 0.05 explain all data in the pH region 2.5–9.5. Equilibrium conditions are illustrated in distribution diagrams and structure proposals are given based on 1H and 13C NMR investigations. In the quaternary H+/H2VO4−/H2O2/Alaser system, six complexes could be found in addition to all binary and ternary complexes over the pH region 2.6–11.1, four with a V/X/Alaser ratio 1 ∶ 1 ∶ 1 and two with a ratio 1 ∶ 2 ∶ 1 (X = peroxo ligand). The formation of the monoperoxo vanadium species is very slow, requiring up to 10 days for complete equilibrium. Significant decomposition of peroxide occurs only in acidic solutions. Chemical shifts, compositions and formation constants for the six quaternary complexes are given, and equilibrium conditions are illustrated in distribution diagrams. The H+/H2VO4−/H2O2/Alaser/Alahis system, where Alahis denotes L-α-alanyl-L-histidine, was briefly investigated and no mixed ligand species were detected.

Interaction of pyridine‐ and 4‐hydroxypyridine‐2,6‐dicarboxylic acids with heavy metal ions in aqueous solutions

AbstractInteractions between pyridine‐2,6‐dicarboxylic acid and 4‐hydroxypyridine‐2,6‐dicarboxylic acid with Cu(II), Pb(II), and Cd(II) ions were characterized in aqueous solutions (20°C; I = 0.4 (KNO3)) by means of dc‐polarography. In solutions with excess of ligand, Cu(II), Pb(II), and Cd(II) form 1:2 complexes with the tridentate dianion of pyridine‐2,6‐dicarboxylic acid (dipic2−) from weak acid to alkaline solutions. The values of log β2 for Cu(II), Pb(II), and Cd(II) are 16.1, 11.8, and 11.0, respectively. The complexing ability of pyridine‐2,6‐dicarboxylic acid is higher in acid solutions and lower in alkaline solutions than that of 4‐hydroxypyridine‐2,6‐dicarboxylic acid. This difference is attributed to the OH‐group, which can deprotonate in basic pH. In acid solutions the OH‐group acts as an electron acceptor and reduces the electron donation available to the nitrogen atom in 4‐hydroxypyridine‐2,6‐dicarboxylic acid, whereas in alkaline solutions the OH‐group is deprotonated, and the deprotonated O− group acts as an electron donor and increases the coordination ability of the ligand. The triple‐deprotonated anion of 4‐hydroxypyridine‐2,6‐dicarboxylic acid (chel3‐) forms a stable diligand complex with Cu(II), the stability constant logarithm being 21.5 ± 0.2.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:625–632, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10203

Complexation of 4f and 5f Cations with Polyoxometalates

Polyoxometalates (POMs) have distinct macromolecular structures, large sizes (6 to 25 Å), high symmetry, large molecular weight (1,000 to 10,000 g/mol), high anionic charges (-3 to - 40) and good aqueous solubility and stability. Metal cations are bound to POMs via surface edge or bridging oxygens in plenary structures or by encapsulation in the defect site for lacunary structures. The binding of Ca2+, Eu3+, UO22+ and Th4+ was studied by solvent extraction, calorimetry and fluorescence with MnMo9O326-, TeMo6O246-, SiW12O404-, P2W18O626-, and P2W17O6110-. Eu3+ was studied as an analog of trivalent actinides as it allows use of macroscale techniques and fluorescence spectroscopy. The sequence of the log β101 values, Ca2+ < UO22+ < Eu3+ < Th4+, reflects ionic interaction and, for UO22+, steric hindrance. For the 1:1 complexes, the residual hydration of Eu3+ is decreased by 5 H2O molecules in the lacunary defect and by 4 in the plenary structure. The binding of all cations is stronger for the lacunary structure POMs. The implications of the data from the M-POM complexation studies and the use of POMs as models for colloid effects in actinide environmental behavior are discussed.

Equilibria and dynamics of some aqueous peroxomolybdate catalysts: a 17O NMR spectroscopic study

The equilibrium speciation at 278 K and the dynamics in the systems pH+ + qMoO42− + rH2O2 + sL ⇌ (H+)p(MoO42−)q (H2O2)r Ls (L = SO42− or Cl−) in 0.3 M Na2(SO4) and 0.6 M Na(Cl) medium has been determined from 17O NMR integral and shift data in the range 0.7 ≤ pH ≤ 4.1 and at excess of peroxide ([H2O2]tot/[Mo]tot = 3). In 0.3 M Na2(SO4) medium species with the following compositions were found: MoX2− (1,1,2,0), MoX2 (2,1,2,0), MoX2S2− (2,1,2,1), MoX2S− (3,1,2,1), Mo2X42− (2,2,4,0), Mo2X4− (3,2,4,0) and Mo2X62− (2,2,6,0), where (Mo) corresponds to MoO42−, (X) to O22− or HOO− and (S) to SO42−. In 0.6 M Na(Cl) medium the diperoxomolybdosulfate complex MoX2S− is replaced with a novel diperoxomolybdochloride complex MoX2Cl− (2,1,2,1), where (Cl) corresponds to Cl−. The numbers in parentheses refer to the values of p,q,r and s in the formula above. The stoichiometries of each complex are given by the abbreviated formula MoqXrSs(2q + 2s − p)– and MoqXrCls(2q + s − p)–. The following formation constants with 3σ were obtained with values for 0.6 M Na(Cl) in parenthesis: log β1,1,2,0 = 11.61 (11.61); log β2,1,2,0 = 13.70 ± 0.10, pKa = 2.09 (13.86 ± 0.10, pKa = 2.25); log β2,1,2,1 = 14.57 ± 0.07 (13.87 ± 0.15 ); log β3,1,2,1 = 15.27 ± 0.17, pKa = 0.70, log β2,2,4,0 = 24.06 ± 0.05 (24.08 ± 0.04); log β3,2,4,0 = 25.99 ± 0.18, pKa = 1.93 (26.23 ± 0.17, pKa = 2.15); log β2,2,6,0 = 24.02 ± 0.15 (23.9 ± 0.3). The pKa value for HSO4− was determined to be 1.06 ± 0.11. At 278 K the MoX2 and Mo2X4 complexes are in chemical exchange and the rate of exchange increases upon protonation. At 312 K there is also measurable exchange between MoX2S and the MoX2 and Mo2X4 complexes. The dynamics in 0.6 M Na(Cl) medium seem to be very similar to those in the sulfate medium.

Characterisation of aqueous peroxomolybdate catalysts applicable to pulp bleachingMulticomponent Polyanions Part 59. For preceding part, see ref. 37.

The equilibrium speciation in the system pH+ + qMoO42− + rH2O2 + sSO42− ⇌ (H+)p(MoO42−)q(H2O2)r(SO42−)s in 0.300 M Na2(SO4) medium at 25 °C has been determined from potentiometric titration data in the ranges 2.0 ≤ pH ≤ 5.5, 5.00 ≤ [Mo]tot/mM ≤ 80.00, 0 ≤ [H2O2]tot/mM ≤ 245 and 273.07 ≤ [SO42−]tot/mM ≤ 320.20. Species with the following compositions were found: MoX− (1,1,1,0), MoX (2,1,1,0), MoX2− (1,1,2,0), MoX2 (2,1,2,0), MoX2S2− (2,1,2,1), Mo2X42− (2,2,4,0), Mo7X6− (8,7,1,0), Mo7X5− (9,7,1,0), Mo7X4− (10,7,1,0) and Mo7X3− (11,7,1,0). The numbers in parentheses refer to the values of p, q, r and s in the formula above. The numbers and charges of molybdenum (Mo), peroxide (X) and sulfate (S) in each species are given in the abbreviated formula MoqXrSs(2q + 2s − p)−. The following formation constants with 3σ were obtained; log β1,1,1,0 = 8.53 ± 0.03, log β2,1,1,0 = 11.22 ± 0.04 (pKa = 2.69), log β1,1,2,0 = 11.61 ± 0.03, log β2,1,2,0 = 13.77 (± 0.06) (pKa = 2.16), log β2,1,2,1 = 14.50 ± 0.06, log β2,2,4,0 = 23.77 ± 0.11, log β8,7,1,0 = 56.71 ± 0.11, log β9,7,1,0 = 62.00 ± 0.05 (pKa = 5.29), log β10,7,1,0 = 65.74 ± 0.06 (pKa = 3.74), log β11,7,1,0 = 68.23 ± 0.08 (pKa = 2.49). Most complexes have been verified by 95Mo NMR, 17O NMR, and the novel MoX2S2− complex also by FTIR spectroscopy.

Mechanisms of sodium and potassium ions transfer facili-tated by dibenzo-15-crown-5 across the water / 1, 2-dichloro- ethane interface using micropipettes

The transfer of sodium and potassium ions facilitated by dibenzo-15-crown-5 (DB15C5) has been studied at the micro-water/1,2-dichloroethane (water/DCE) interface supported at the tip of a micropipette. Cyclic voltammetric measurements were performed in two limiting conditions: the bulk concentration of Na+ or K+ in the aqueous phase is much higher than that of DB15C5 in the organic phase (DB15C5 diffusion controlled process) and the reverse condition (metal ion diffusion controlled process). The mechanisms of the facilitated Na+ transfer by DB15C5 are both transfer by interfacial complexation (TIC) with 1:1 stoichiometry under these two conditions, and the corresponding association constants were determined at log β1 = 8.97 ±0.05 or log β1 = 8.63 ±0.03. However, the transfers of K+ facilitated by DB15C5 show different behavior. In the former case it is a TIC process and its stoichiometry is 1:2, whereas in the latter case two peaks during the forward scan were observed, the first of which was confirmed as the formation of K+(DB15C5)2 at the interface by a TIC mechanism, while the second one may be another TIC process with 1:1 stoichiometry in the more positive potential. The relevant association constants calculated for the complexed ion, K+(DB15C5)2, in the organic phase in two cases, logβ2, are 13.64 ±0.03 and 11.34 ±0.24, respectively.

The solubility of iron in seawater

Abstract The solubilities of iron(III) hydroxides in seawater were determined in Gulf Stream seawater as a function of pH (2 to 9), temperature (5 to 50 °C) and salinity (0 to 36). Our results at S=36 and 25 °C near a pH of 8 are in agreement with the measurements of Byrne and Kester [Mar. Chem. 4 (1976a) 255] and Kuma et al. [Limnol. Oceanogr. 41 (1996) 396] (0.2 to 0.3 nM). The solubilities at 5 °C are considerably higher than at 25 °C and decrease with a decrease in salinity. Near a pH of 8, the solubilities as a function of temperature (T/K) and ionic strength [I=19.922S/(1000−1.005S)] can be estimated from log [ Fe ( III )]=−10.53+322.5/T−2.524I 0.5 +2.921I (σ=0.2) The results at low pH (2 to 5) and S=36 have been used to determine the limiting solubilities of Fe(OH)3(s) which have been fitted to the equation (σ=0.08) log K Fe ( OH ) 3 *=−9.17+3993/T The values of KFe(OH)3* are in good agreement with those determined in 0.7 m NaCl. The solubilities as a function of pH, temperature and salinity have been used to determine the stability constants for the formation of Fe(OH)2+, Fe(OH)2+ and Fe(OH)3. The hydrolysis constants at I=0.74 (S=36) have been fitted to the equations log β 1 *=1.86−1300/T (σ=0.1) log β 2 *=0.18−1997/T (σ=0.2) log β 3 *=−2.47−3185/T (σ=0.8) The results for log β1* and log β2* at 25 °C are in reasonable agreement with the values in 0.7 m NaCl. The value of log β3* in seawater is larger than the value in 0.7 m NaCl due to the formation of Fe(III) complexes with organic matter. The higher solubilities in seawater (0.3–0.5 nM) compared to the values in 0.7 m NaCl (0.011 nM) are due to the formation of Fe3+ complexes (FeL) with natural organic ligands (L). By diluting seawater (S=36) with 0.7 m NaCl, we have been able to show that the solubilities approach the values in NaCl at the same ionic strength and temperature. The differences in the solubility of Fe in seawater and 0.7 m NaCl near a pH have been used to calculate ligand concentrations [L′]=0.1–0.2 nM (not complexed with iron) using a literature value of the stability constant (K′FeL=1011.5). The results at different temperatures have been used to determine a value of ΔH=7±5 kcal mol−1 for the formation of FeL.

Thermodynamic stability and kinetic inertness of MS-325, a new blood pool agent for magnetic resonance imaging.

Stability constants were measured for complexes formed between a modified DTPA ligand and the metal ions Gd(III), Eu(III), Fe(III), Ca(II), Cu(II), and Zn(II) at 25 degrees C in 0.1 M NaClO4. The gadolinium complex of this ligand is MS-325, a novel blood pool contrast agent for magnetic resonance imaging currently undergoing clinical trials. Stability constants were determined by 4 different methods: direct pH titration, pH titration with competition by EDTA, competition with DTPA using an HPLC-MS detection system, and competition with Eu(III) by monitoring equilibrium by luminescence spectroscopy. The 1:1 stability constants, log beta101, are the following: Gd, 22.06 (23.2 in 0.1 M Me4NCl); Eu, 22.21; Fe, 26.66; Ca, 10.45; Cu, 21.3; Zn, 17.82. The exchange kinetics of the Gd complex, MS-325, with the radioactive tracer (152,154)Eu were studied at 25 degrees C in 0.1 M NaClO4. The exchange reaction has acid-dependent and acid-independent terms. The rate expression is given by the following: R = k(a)[GdL][H]2 + kb[GdL][Gd][H] + kc[GdL][Gd]. The rate constants were determined to be the following: k(a) = 1.84 x 10(6) M(-2) x min(-1), kb = 2.87 x 10(3) M(-2) x min(-1), kc = 3.72 x 10(-3) M(-1) x min(-1). MS-325 is 2-3 times more stable than GdDTPA at pH 7.4 and is 10-100 times more kinetically inert.

Hydrolysis of [Pt(dien)H2O]2+ and [Pd(dien)H2O]2+ complexes in water

The hydrolysis of the [Pt(dien)H2O]2+ and [Pd(dien)H2O]2+ complexes has been investigated by potentiometry at 298 K, in 0.1 mol dm−3 aqueous NaClO4. Least-squares treatment of the data obtained indicates the formation of mononuclear and μ-hydroxo-bridged dinuclear complexes with stability constants: log β11 = −6.94 for [Pt(dien)OH]+, log β11 = −7.16 for [Pd(dien)OH]+, and also log β22 = −9.37 for [Pt2(dien)2(OH)2]2+ and log β22 = −10.56 for [Pd2(dien)2(OH)2]2+. At pH values > 5.5, formation of the dimer becomes significant for the PtII complex, and at pH > 6.5 for the PdII complex. These results have been analyzed in relation to the antitumor activity of PtII complexes.

From 8-hydroxy-5-sulfoquinoline to new related fluorogenic ligands for complexation of aluminium(III) and gallium(III)

The hexadentate tripodal ligand O-TRENSOX (already known as a siderophore), incorporating three 8-hydroxy-5-sulfoquinoline (8-HQS) subunits, was investigated as a potential fluorogenic ligand of Al(III) and Ga(III). For the sake of comparison, every chelation study was also carried out with n-BUSOX, a ligand similar to one arm of O-TRENSOX. Chelations were studied at the optimal pH for fluorescence emission: pH = 4 for Al(III) and pH = 2 for Ga(III). An outstanding ‘tripod’ effect is exhibited by the values of the stability constants: with O-TRENSOX, log β111 = 24.8 for Al(III) and 33.7 for Ga(III), whereas with n-BUSOX, log β110 = 8.6 for Al(III) and 11.6 for Ga(III) at 25 °C. O-TRENSOX is nearly as efficient for Ga(III) chelation as for Fe(III). When increasing the [metal]/[ligand] ratio, fluorescence emission rose until either 1 : 1 chelation with n-BUSOX or 3 : 1 chelation with O-TRENSOX was achieved. Then, the resulting fluorescence intensity levelled off. The fluorescence emission intensity from n-BUSOX chelates was observed to be tenfold larger than that from O-TRENSOX chelates, suggesting that a self-quenching process occurs within the latter complexes. In terms of selectivity, ions such as Zn(II) or Cd(II), known to form strongly fluorescent complexes with 8-HQS, are not chelated at pH = 2 by n-BUSOX and O-TRENSOX. Thus, they are not potential interferences for Ga(III) determination, whereas Fe(III) strongly interferes, quenching the fluorescence. Conversely, although less stable at pH = 4, the chelates of Zn(II) and Cd(II) are possible interferences for Al(III) determination because of their strong fluorescence emission.

Capillary zone electrophoretic (CZE) study of uranium(VI) complexation with humic acids

The interaction of UO2 2+ with various humic acids (HA's) has been studied by capillary zone electrophoresis (CZE). The experiments were done in 10 mM acetate buffer with pH 3.3 and 4.0, to avoid hydrolysis of uranium. It was found that in slightly acidic media and low HA concentration (<3 mM), two complexes with uranium(VI) are formed by fast kinetics and uranyl migrates as cationic species. Electrophoretic mobilities are decreasing with the increasing HA/uranium ratio and a low soluble neutral compound is also formed. In addition, it was found that at HA concentrations higher than 3 mM negatively charged species are formed. Similar results were obtained for HA's of different origin (soil, peat, coal derived, IHSS standards). Conditional stability constants of the complexes UO2 2+-HA for Fluka I HA, were estimated to be log β1 = 4.18±0.06 and log β2 = 7.28±0.18.

Studies On Some Acid Divalent-Metal Nitrilotriacetate Complexes

IR and 1H-NMR studies on nitrilotriacetic acid (H3NTA) suggest that the acid exists in the zwitterion form, which allows the existence of intermolecular hydrogen bonding. A tetrahedral structure is established for eleven (1:1) anhydrous acid-metal (II) nitrilotriacetates complexes. The ten Dq values for the colored complexes were determined spectrophotometrically. The pKa values for the eleven acid metal complexes [M(HNTA)].(OH2)3] were determined and compared with the corresponding pKa values of the [M(OH2)n]+2 ions and also with the log β1 values of the corresponding [M(NTA)]- complexes. X-ray diffraction studies on the ligand and on eight of these complexes are described.

Lanthanide Podates with Programmed Intermolecular Interactions: Luminescence Enhancement through Association with Cyclodextrins and Unusually Large Relaxivity of the Gadolinium Self-Aggregates

The synthesis of the phenyl anchored podand H4L1 fitted with four 3-carboxylate pyrazole arms and programmed for intermolecular interactions is reported, and its protonation constants are determined. Interaction with Ln3+ ions (Ln = La, Eu, Lu) in dilute aqueous solutions leads to complexes with 1:1 and 1:2 metal−ligand stoichiometry. The stability constants are in the range log β110 = 12.7−13.5 and log β120 = 22.5−23.8 (pLn values in the range 9−10). The podates display a fair sensitization of the metal-centered luminescence with an absolute quantum yield of 5% in case of TbIII. The average numbers of water molecules coordinated to the LnIII ion amount to 3.8 and 4.9 for the 1:1 Eu and Tb podates, respectively, as determined by lifetime measurements. The addition of β- and γ-cyclodextrins to the 1:1 podates results in a strong association with the host, mainly through the phenyl anchor (Ln = Tb, log K11 = 5−6 depending on the cyclodextrin) and, for the Tb complex, to a large increase in luminescence intensity at physiological pH. Self-aggregation of the podates occurs at concentration larger than 3 × 10-5 M. This process is characterized by luminescence, using a pyrene probe, light-scattering measurements, and transmission electron microscopy. The novelty of the reported systems is their ability to self-aggregate into nanometric, rigid, and spherical particles in a controlled way (mean diameter: 10, 60, and ∼300 nm), opening large perspectives for various applications. In particular, a record-high relaxivity (r1 = 53 mM-1 s-1 at 20 MHz, T = 25 °C) is observed for the aggregates of 1:2 Gd podate, which is not modified upon addition of an equimolar quantity of ZnII.

Pyrocatechol Violet Complexation at the Boehmite–Water Interface

Acid/base reactions and pyrocatechol violet complexation at the boehmite–solution interface have been investigated in 0.10 M K(Cl) solution at 298.2 K in the range 5.0≤−log h≤9.0. Equilibrium measurements were performed as potentiometric titrations complemented by spectrophotometric analysis of a ligand (batch adsorption experiments). The experimental data were evaluated on the basis of the extended constant capacitance model, allowing for inner-sphere and/or outer-sphere complexation. The acid/base properties are described by the equilibria: H++≡AlOH⇋ ≡AlOH2+; log β1,1,0(int)=7.46±0.04 and ≡AlOH ⇋≡AlO−+H+; log β−1,1,0(int)=−9.87±0.12. The specific capacitance was determined as 1.00 F m−2. The binding of pyrocatechol violet {PCV, 2-[(3,4-dihydroxyphenyl)(3-hydroxy-4-oxocyclohexa-2,5-diene-1-ylidene)methyl]benzenesulfonic acid}, H4L, was described by the formation of a single inner-sphere complex according to the reaction ≡AlOH+H4L⇋≡AlL3−+3H++H2O. Allowing for a charge distribution of this complex between the inner plane and β-plane (−2, −1), a significant improvement of the fit was obtained. The adsorbed complex exhibited a dark blue color over the pH range 5–8.5, indicative of proton loss from the 1,2-dihydroxyl moiety. Furthermore, DRIFT spectra showed the bonding environment of PCV bound to the surface to exhibit similarities with corresponding catechol adsorption to different aluminium (hydr)oxides. These spectral features turned out to be very similar to soluble catechol complexes of Al(III). Thus, it is suggested that PCV forms a mononuclear chelating complex at the boehmite–water interface. The maximum surface coverage reached was ca. 33%, indicating that the high negative charge of the species may result in surface charge “saturation” rather than saturation of surface binding sites. Steric hindrances caused by the large size of PCV may also contribute to the low surface coverage.

Uranium(VI) complexation with citric, humic and fulvic acids

The binding of uranium(VI) by Suwannee River humic and fulvic acids was studied at pH values of 4.0 and 5.0 in 0.10 M NaClO4using an ion-exchange technique. Few data sets currently exist for metal binding to different molecular weight fractions from the same source. The complexation of U(VI) by citric acid was also studied under the same experimental conditions in order to "calibrate" the experimental and modeling approaches. For the citric acid system, the experimental results were analyzed using Schubert´s ion-exchange method, which indicated the formation of only a 1:1 uranyl-citrate complex. Close agreement was found for the values of log β1,1(6.69±0.03 at I = 0.10) determined from nonlinear regression of data collected at pH values of 4.0 and 5.0. This value represents a more direct measurement of the binding constant for the 1:1 uranyl-citrate complex than do other existing literature values derived from experimental data requiring the simultaneous consideration of 1:1 and 2:2 species.Both humic and fulvic acids were demonstrated to strongly bind U(VI), with humic acid forming slightly stronger complexes and exhibiting greater pH dependence. Analyses of the data for the humic and fulvic acid systems using the Schubert´s equation previously applied to the citrate system result in an apparent nonintegral number of ligands binding the uranyl ion. Schubert´s method is only appropriate for interpreting mononuclear complexes with integral moles of binding ligands. Thus, a more elaborate binding model was required and the data were interpreted assuming either: (1) a mixture of 1:1 and 1:2 uranyl-ligand complexes or (2) a limited number of high affinity sites forming a 1:1 complex. While both of these modeling approaches are shown to provide excellent fits to the data, the second is deemed more appropriate given the large size of humic and fulvic acid molecules as well as previous results obtained with other metal cations, such as Cu(II).