Log Β2 Research Articles

Synthesis and iron(III) complexing ability of CacCAM, a new analog of enterobactin possessing a free carboxylic anchor arm. Comparative studies with TRENCAM

A new tricatecholate, CacCAM, has been synthesized by attachment of three catecholamide subunits to a CO2H-functionalized triamine backbone. The solution coordination chemistry of the ligand and its iron(III) complex have been investigated by potentiometric, spectroscopic and kinetic methods. The results are compared to those obtained with TRENCAM, which possesses the same catecholamide subunits, but a TREN [tris(2-aminoethyl)-amine] backbone. The stability constant (log β110=42.9, pFe=27.5) is close to that of TRENCAM (log β110=43.6, pFe=27.8), showing that a change of backbone does not significantly alter the iron chelating ability of the ligand. Kinetics of iron exchange between Fe(III)–EDTA and CacCAM or TRENCAM involves similar rate constants (16±1 and 14±2 M−1 s−1, respectively). EPR data show that the iron(III) does not have the same distorted rhombic geometry in the two complexes. Fe(III)–CacCAM has been tested as a source of iron in nutritional experiments with Arabidopsis thaliana plant cells: its efficiency is good, comparable to that of Fe(III)–EDTA, the most widely used iron complex for plant nutrition.

The formation of mixed-hydroxo complexes of Cm(III) and Am(III) with humic acid in the neutral pH range

The complexation of humic acid with Cm(III) and Am(III) is studied in the neutral pH range from 6 to 10 in 0.1 M NaClO4under Ar-atmosphere. Cm(III) and Am(III) species are characterized and quantified by time-resolved laser fluorescence spectroscopy (TRLFS) and UV/Vis absorption spectroscopy, respectively. The formation of ternary humate complexes, i.e. hydroxo-humate species, is ascertained besides the well known binary complex AnHA(III) (An = Cm(III), Am(III)) by spectroscopic speciation in aid of radiometric quantification. The pH dependent change in concentrations of individual Cm(III) and Am(III) species corroborates ternary humate complex formation: An(OH)HA(II) and An(OH)2HA(I), with stability constants evaluated to be log β111= 12.82 ± 0.11 and log β121= 17.53 ± 0.13 for Cm(III) and log β111= 12.71 ± 0.17 and log β121= 17.40 ± 0.21 for Am(III). The formation of ternary humate complexes culminates in the strong interaction of trivalent actinide ions with humic acid in the neutral pH range as compared to the binary complexation alone. The results are compared with a previous study on the Cm(III) interaction with humic colloids in a real groundwater system.

Separation of lanthanum(III) and barium(II) as their thenoyltrifluoroacetone complexes with dibenzo-18-crown-6 by means of synergistic extraction.

A new method for the separation of lanthanum(III)and barium(II)as their thenoyltrifluoroacetone(TTA)complexes with dibenzo-18-crown-6(DB18C6)in o-dichlorobenzene has been established by means of synergistic extraction and back-extraction combined with inductively coupled plasma atomic emission spectrometry(ICP-AES).When the mixtures of La(III)and Ba(II)were extracted for 5min at pH 4.5, only lanthanum(III)was extracted quantitatively, whereas barium(II)remained in the aqueous phase.After the phases were separated, barium(II)was extracted quantitatively for 5min at pH 7.9 again.Then, the two phases were each shaken with 0.1M HCl in order to back-extract lanthanum(III)and barium(II)from the organic phases;both metal ions were determined by ICP-AES.In the process, lanthanum(III)and barium(II)TTA chelates in o-dichlorobenzene formed stable adducts with DB18C6(La(TTA)3·nDB18C6 and Ba(TTA)2·nDB18C6, n=0-2).The stability constants(βn)of the adducts determined by means of curve-fitting method were log β1=3.7 and log β2=5.9 for lanthanum(III), and log β1=3.8 and log β2=7.9 for barium(II).The extraction constant(log K)of lanthanum(III)adduct was −3.7.

Equilibrium and kinetic studies on the complexation of boric acid with chromotropic acid

The complexation of boric acid with chromotropic acid in aqueous solution was examined thoroughly by 11B NMR measurements. Two peaks with chemical shift values of δ −17.7 and −18.0 were observed besides the free boric acid/borate peak and ascribed to the 1∶1 and the 1∶2 complexes, respectively. The 1∶2 complex is formed in acidic solution, while the 1∶1 complex prevails in a higher pH range. The formation constants for these complexes were evaluated based on the signal intensities of 11B NMR spectra to be log β1 = −1.57 and log β2 = 2.35, which are well consistent with those reported previously as well as that (β2) obtained kinetically in this work. The chromatographic separation of the 1∶2 complex from the other species enabled a kinetic study of the reaction which revealed that the reaction for 1∶1 complex formation takes place much faster than that for 1∶2 complex formation. The pH dependences of the rate constants of the forward and backward reactions of the 1∶2 complexation could be interpreted by the catalytic role of hydrogen ions in the reactions. Plausible mechanisms for both the reactions of 1∶2 complex formation and decomposition were proposed. On the basis of the equilibrium and kinetic information on the complexation, the optimum conditions for practical applications of the ligand so far reported could be well understood.

Investigation of neptunium(VI) complexation by SiW11O398- by visible/near infrared spectrophotometry and factor analysis

Neptunium(VI) complexation by a lacunary heteropolyanion (SiW11O398−) in an aqueous medium at pH 1 was investigated by spectrophotometry in two regions of the spectrum: in visible light (540–670 nm) and in the near infrared (1120–1260 nm). Principal components analysis (PCA) revealed the formation of two species depending on the additive ligand in solution: a NpO2(SiW11O39)6− complex and the free species NpO22+ that was initially present at pH 1. Modeling factor analysis (MFA) was used to calculate a similar absolute constant for both wavelength regions: log β1=11.6±0.1. This technique was also used to determine the spectrum of the NpO2(SiW11O39)6− complex formed in aqueous solution.

The directional reaction of hydrazine with silver complexes. Part 2. Influence of acidity and temperature

The influence of acidity and temperature on the reaction of two-coordinate silver complexes with N2H4 has been studied. The N2(F)% which represents the percentage of N2 formed by the four-electron oxidation of N2H4 [Reaction (A)] was greatly increased by the presence of a trace of CuII ion in the system. The N2(F)% was also enhanced by increasing the pH and temperature in the absence of CuII ion. In addition, the N2(F)% was linearly related to log β2 for the silver complexes. The log of the N2(O)% which represents the percentage of N2 formed by the one-electron oxidation of N2H4 [Reaction (B)] was linearly related to the 1/logβ2 value in the presence of CuII ions.

Effective complex formation in the interaction of 1,2-dimethyl-3-hydroxypyrid-4-one (Deferiprone or L1) with uranium(VI)

In an effort to develop new chelating agents for the decorporation of uranium and other actinides, the interaction of the clinically used 1,2-dimethyl-3-hydroxypyrid-4-one (Deferiprone or L1) with hexavalent uranium was investigated by using UV-VIS spectroscopy and solubility measurements. The complex stoichiometry estimation carried out by the Job plot method indicated that under normal conditions up to pH 8.0 a 1[U(VI)]∶1[L1] complex is formed. The stability constant of the UO2L1+ complex was determined by spectroscopic and solubility experiments and found to be log β11=9.1±0.3. The molar extinction coefficient at pH 7.6 for the complex at 500 nm was estimated to be 650 l·mol−1·cm−1. At ligand concentrations higher than 6·10−4 mol·l−1 the formation of a precipitate was observed. The stoichiometry UO2(L1)2 was identified following FTIR measurements of the red precipitate and UV/VIS spectroscopy after dissolution.

13C and 27Al NMR and Potentiometric Study on the Interaction between Aluminium Ions and Quinolic Acid in Acidic Aqueous Solutions

The interaction between aluminium ion (Al) and quinolic acid (L) in acidic aqueous solution was investigated by poten-tiometry and 13C and 27Al NMR spectroscopy. In the 27Al NMR spectra, two peaks were observed at 8 and 15.6 ppm, which were assigned to AlL and AlL2 complexes, respectively. The 13C NMR spectra provide clear evidence that the L acts as a bidentate ligand and that the L coordinates with a nitrogen atom and an oxygen atom of the adjacent carboxylic group to form a chelate complex with a five-membered ring. From a potentiometric study, the formation constants (log β1 and log β2) for the AlL and AlL2 complexes were estimated to be 4.52±0.02 and 7.99±0.05, respectively.

Raman spectroscopic investigation of chromium(VI) equilibria — another look

Quantitative Raman intensity data for aqueous CrVI solutions were obtained with the object of modelling the equilibria involved. Raman scattering data for two series of chromate(VI) solutions containing 12 and 18 mM CrVI, in the pHc range ca 3–10 (0.10 M NaCl), were subjected to computer modelling calculations using the program PHAB. The model which assumes that CrO42− undergoes protonation to HCrO4− (log β11 = 6.01 ± 0.24) and condensation to Cr2O72− (log β22 = 13.87 ± 0.36) can be fitted better to the experimental intensity data than one which ignores HCrO4−. Copyright © 1999 John Wiley & Sons, Ltd.

Potentiometric study of Cd(II) and Pb(II) complexation with two high molecular weight poly(acrylic acids); comparison with Cu(II) and Ni(II)

The cadmium (II) or lead (II) complex formation with two poly(acrylic acids) of high molecular weight (Mw=2.5×105 and 3×106) was investigated in dilute aqueous solution (NaNO3 0.1 mol l−1; 25°C). Potentiometric titrations were carried out to determine the stability constants of the MA and MA2 complex species formed. Bjerrum’s method, modified by Gregor et al. (J. Phys. Chem. 59 (1955) 34–39), for the study of polymeric acids was used. The results were compared to those previously obtained in the same conditions with copper (II) and nickel (II) [1]. It appeared that the two polymers under study present similar binding properties and that the stability constants of the complex species formed increased in the following order, depending on the metal ion: Ni(II)<Cd(II)<Cu(II)<Pb(II). Lead (II) ions seemed to be particularly well bound to PAAs (the global stability constant log β102 was found to be close to 7.0) and allowed the formation of the predominant PbA2 species in a quite large pH domain. Finally, the greater stability of PAA complexes compared to those of their monomeric analogs, glutaric and acetic acids, was confirmed.

Hafnium Hydroxide Complexation and Solubility: the Impact of Hydrolysis Reactions on the Disposition of Weapons-Grade Plutonium

AbstractThe stability constants for the complexation of hafnium by hydroxide ions is investigated by potentiometric titration over a range of ionic strengths (1m = 0.1 to 6.6 molal). The stability constants are determined from the titration data using the HYPERQUAD suite of programs. The stability constants at infinite dilution are determined using the Specific Ion Interaction Theory from the stability constants determined by titration. The results are shown with the error given as 2 standard deviations.log β11 (Hf(OH)3+) = 13.84 ± 0.54 log β12 (Hf(OH)22+) = 25.71 ± 0.39 log β13 (Hf(OH)3+) = 36.24 ± 0.88 log β14 (Hf(OH)40) = 45.52 ± 0.80The solubility product of Hf(OH)4 (s) is determined in 0.1 M NaC1O4 by measuring the total hafnium in solution that is in equilibrium with an excess of hafnium hydroxide solid under an argon atmosphere. The total Hf concentration is determined by ICP-AES. The solubility product is determined using the stability constants measured for the H f hydrolysis products in 0.1 M NaClO4. The precipitate examined is confirmed to be a hydroxide by IR spectroscopy. For Hf(OH)4 (s) in 0.1 M NaC1O4, the solubility product is log Ksp (Hf(OH)4 (s)) = −51.8 ± 0.5The solubility and stability constants determined are used, along with literature values for plutonium solubility and complexation constants, to examine the behavior of hafnium and plutonium under the conditions expected at Yucca Mountain.

Potentiometric Determination of Silver Thiolate Formation Constants Using a Ag2S Electrode

Formation constants for silver thiolates were obtained by titration of the ligand in a constant temperature, ionic strength and pH medium and measuring the potential change at a Ag2S electrode. A non-linear equation was derived from which the first and second silver formation constants, β1 and β2′, and the sulfide group acid dissociation constant, Ka′, were determined. An overall estimate of the uncertainty in the derived parameters was obtained using a Monte Carlo approach. The procedure was compared to a previous work on AgHS°. Log β1′, log β2′ and - log Ka′ results were obtained for cysteine (11.9 ± 0.5, 15.2 ± 0.4, 7.8 ± 0.1), glutathione (12.3 ± 0.3, 14.3 ± 0.8, 8.8 ± 0.3) and 3-mercaptopropanoic acid (12.0± 0.4, 14.0 ± 0.4, 10.5 ± 0.3) at 20 °C and 0.01 m ionic strength.

Lanthanide complexes with a p-tert-butylcalix[4]arene fitted with phosphinoyl pendant arms †

The lower-rim substituted calix[4]arene, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy)calix[4]arene (L) has been synthesized and characterised by the single-crystal structure of its acetonitrile adduct, L·2MeCN (monoclinic, space group P21/c). The ligand adopts a cone conformation and a Δ enantiomeric form with the four phosphinoyl arms in a δδδδ configuration. The cone conformation is maintained in organic solution where L displays a time-averaged C4 symmetry. Trivalent lanthanum ions interact with L in acetonitrile to yield both 1∶1 (log β1 = 11.4 ± 1.5) and 1∶2 (log β2 = 19.6 ± 1.8) complexes; two forms of the 1∶1 complex are identified depending on the water content of the solutions. A photophysical study of both the ligand- and metal-centred luminescence of complexes of La, Eu and Tb points to L having a moderate quantum yield (ca. 10%, ligand-centred luminescence) and being a poor sensitiser of europium and terbium ions. It confirms the presence of differently solvated 1∶1 (and 1∶2) complexes, depending on the solvent composition. The lifetimes of the metal-centred luminescence of the unhydrated 1∶1 and 1∶2 complexes are long, in the range 1.4–2.4 ms for Eu and 1.7–7.3 ms for Tb, which indicates that the lanthanide(III) ions are well encapsulated in the cavity formed by the donor groups of the calix[4]arene molecule(s).

Co-ordination chemistry of macrocyclic compounds with dangling phosphines. Unusual NMR shifts in metallo-calix[4]arenes †

The chelating behaviour of three polyphosphines, cone-5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(diphenylphosphinomethoxy)calix[4]arene L1, cone-5,11,17,23-tetra-tert-butyl-25,26,27-tris(diphenylphosphinomethoxy)-28-methoxycalix[4]arene L2, and cone-5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinomethoxy)-27,28-dihydroxycalix[4]arene L3, has been investigated. When [Mo(CO)3(C7H8)] and tetraphosphine L1 are heated together under reflux in tetrahydrofuran (THF) complex [Mo(CO)3L1] 1 is formed, for which the calixarene behaves as a fac-bonded tridentate ligand with one phosphine remaining free. Similar fac-chelating behaviour is found with [Mo(CO)3L2] 2, which is obtained from triphosphine L2. Formation of this latter complex is accompanied by the calixarene matrix adopting a partially flattened-cone conformation. In contrast, the conventional cone conformation is maintained in the trinuclear complex [(AuCl)3L2] 3, obtained quantitatively by treating L2 with [AuCl(THT)] (THT = tetrahydrothiophene). Reaction of L1 with [RuCl2(DMSO)4] (DMSO = Me2SO) in CH2Cl2 results in selective formation of the deep purple complex [RuCl2L2] 4 built around a fac-trigonal bipyramidal RuCl2P3 structure. Complex 4 reacts reversibly and stepwise with two equivalents of CH3CN. The calculated stability constants, as determined from a spectrophotometric titration, are log β1 = 9.1 and log β2 = 12.4. The proximally substituted calixarene L3 reacts with [PtCl2(COD)] (COD = cycloocta-1,5-diene) to afford the chelate complex cis-[PtCl2L3] 5. As revealed by an X-ray diffraction study, the P–Pt vectors point away from the calixarene axis in the solid state. The axial H atom of the C6H2CH2 group located between the two phosphine units of L3 undergoes a significant low-field shift upon complexation (δ 7.32 vs. 4.48 for free L3) presumably due to interaction with the lone pairs of the two neighbouring O-atoms. Complex 5 displays dynamic behaviour in solution, which can be rationalized as follows: (i) a fast flip-flop motion of the hydroxyl groups at low temperature, alternately forming hydrogen bonds with each of two neighbouring phenolic oxygens; (ii) a reversible inversion of the phenol ring through the lower-rim annulus, triggered by breakage of the hydrogen bonds at higher temperature. Reaction of [PtCl2(COD)] with one equivalent of L1, followed by in situ oxidation with NH2CONH2·H2O2, results in formation of a chelate complex, containing two proximal phosphines bonded to platinum as in 5 and two pending CH2P(O)Ph2 phosphine oxides. Stepwise reaction of [PtCl2(COD)] with one equivalent of L1 and two equivalents of [AuCl(THT)] gives a cis complex in which the platinum atom is again bonded to two proximal phosphines and the two AuCl units to the other two phosphine arms. As in 5, an anomalous low-field shift is observed for the axial C6H2CH belonging to the platinocycle of these complexes.

Copper(II) Complexation Properties and Surfactant Activity of 3-[N,N-Bis(2-hydroxyethyl)amino]-2-hydroxypropanesulfonic Acid andN-(2-Hydroxyethyl)piperazine-N′-2-hydroxypropanesulfonic Acid pH Buffers Which May Affect Trace Metal Speciation inin VitroStudies

Disadvantages of the some zwitterionic pH buffers are (i) that they can interact with metal ions as well as protons, and (ii) that they may have a surfactant effect in chemical orin vitrobiological or biochemical studies. This has to be taken into account when a buffer is selected. Here, the copper-complexing capacity and the surfactant activity of three compounds, 3-[N,N-bis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO),N-(2-hydroxyethyl)piperazine-N′-(2-hydroxypropanesulfonic acid) (HEPPSO), and piperazine-N,N′-bis(2-ethanesulfonic acid) (Pipes), were investigated. Global stability constants (log βabc) of copper(II)–buffer complexes were determined, at 25°C, 0.5 M ionic strength, and at 0.8 mM buffer concentration, by pH and pCu ion-selective electrode measurements. Here, βabccorresponds to the equilibrium: aCu2++ bL−+ cH+↔ (CuaLbHc)(2a−b+c); HL = DIPSO or HEPPSO; c: +1 = proton; −1 = hydroxide. Using SUPERQUAD constants were calculated, giving: DIPSO: log β110= 5.02, log β120= 8.99, log β130= 13.0, log β140= 16.3, log β14−1= 9.26, log β14−2= 0.645, log β150= 20.5, log β160= 24.3, log β16−1= 16.1, log β16−2= 8.98; HEPPSO: log β110= 4.29, log β120= 8.35, log β130= 12.1, log β140= 15.9, log β150= 19.6, log β160= 23.4, log β16−1= 14.9. The pKavalues were determined at higher buffer concentrations, giving a value 7.33 for DIPSO and 7.84 for HEPPSO at 2.0 mM buffer concentration. Effects of buffer concentration on stability and acidity constants were investigated and compared with measurements using voltammetric and potentiometric stripping analysis, confirming no copper(II) complexation by Pipes. Surfactant activities were determined using alternating current polarography, confirming marked surface activity of 10 mM of DIPSO or HEPPSO.

Spectrophotometric Investigation of Uranil(II)−Rutin Complex in 70 Ethanol

The composition and stability constant of a UO2(II)-rutin complex in 70% ethanol were determined by suitable spectrophotometric methods and pH measurement. UO2(II) ion and rutin (3,3‘,4‘,5,7-pentahydroxyflavone-3-rhamnoglucoside) form a 1:1 complex in which the UO2(II) ion is linked to rutin through the carbonyl and 5-hydroxyl group. The concentration stability constant of the complex, log β1, ranged from 6.57 at pH 4.00 to 4.72 at pH 7.00. Conditions for spectrophotometric determination of rutin, by complex formation with UO2(II) ion, were investigated. Beer's law was obeyed in the concentration range from 1.0 × 10-5 to 2.0 × 10-4 M for rutin. Determination of rutin in Rutinion forte tablets was demonstrated. Keywords: Complex; rutin; uranilnitrate; stability constant; spectrophotometric methods

Complexation equilibrium between iron(III) and N,N'-bis(2-hydroxyphenylmethyl)-N,N'-bis(2-pyridylmethyl)-1,2-ethanediamine

Complexation equilibrium between iron(III) and N,N' -bis(2-hydroxyphenylmethyl)-N,N' -bis(2-pyridylmethyl)-1,2- ethanediamine (H2bbpen), a colorless hydrophobic divalent hexadentate ligand, and potential use of the ligand for the spec- trophotometric determination of iron(III) in aqueous solution was investigated. In the pH range 2.0 - 3.0, Fe(III) forms stable 1:1 complex with H2bbpen, and Fe(III) can be determined selectively as the purple Fe(bbpen) + complex (λmax = 560 nm, e = 4.3 〈 103 dm3 mol-1 cm-1, log β1 = 32.6 ∠ 0.1). In this system, linear calibration range of Fe(III) was 5 〈 10-6 - 2 〈 10-4 mol dm-3 (0.3 - 12 µg cm-3) and detection limit was 3 〈 10-6 mol dm-3 (0.2 µg cm-3). Furthermore, most of foreign metal cations did not influence largely the determination of Fe(III).

Hydrolysis of (CH3)Hg+ in Different Ionic Media: Salt Effects and Complex Formation

The hydrolysis of monomethylmercury(II) was studied potentiometrically, in NaNO3, Na2SO4, and NaCl aqueous solution, in a wide range of ionic strengths (NaNO3, 0 ≤ I ≤ 3.25; Na2SO4, 0 ≤ I ≤ 1; NaCl, 0 ≤ I ≤ 3 mol dm-3) and at t = 25 °C. For the reaction (CH3)Hg+ = (CH3)Hg(OH)° + H+, we found log K1 = −4.528 (I = 0 mol dm-3). The species [(CH3)Hg]2(OH)+ was also found, with log β2 = −2.15. Monomethylmercury(II) forms quite strong complexes with Cl- (log K = 5.45, I = 0 mol dm-3) and SO42- (log K = 2.64, I = 0 mol dm-3). The dependence on ionic strength of formation constants was considered by using a Debye−Hückel type equation. Hydrolysis and complex formation constants (at different ionic strengths) obtained were used to calculate the interaction parameters of Pitzer equations.

Equilibria of the H+-MoO2−4-CH3PO2−3 system in aqueous 1.0 M Na(Cl) medium

The equilibria pH++qMoO2−4+rCH3PO2−3⇄(H+) p(MoO2−4)q(CH3PO2−3) r have been investigated at 25.0°C in 1.000 M Na(Cl) by the combined emf-NMR method. Quantitative analysis of the emf and 31P NMR data confirmed the existence of the following ternary species, denoted by (p, q, r) according to the general equilibria above: (10, 5, 2), (11, 5, 2), (11, 7, 1), (12, 7, 1), and (12, 6, 1). Least-squares calculation gave log β10, 5, 2=69.51±0.01, log β11, 5, 2=71.07±0.08, log β11, 7, 1=72.69±0.04, log β12, 7, 1=76.23±0.05, and log β12, 6, 1=70.31±0.05. The formation constants of the (p, 5, 2) species of the current system and the molybdoselenite system correlate with the pKa of the heteroatom source.

Mechanisms of neurite elongation induced by proteasome inhibitor

Equilibria of cobalt(II) perchlorate with lithium chloride in 0.1 M LiClO4 acetone solution have been investigated by means of potentiometry and spectrophotometry at 25.0°C. By the addition of a large excess of medium salt (LiClO4), the ionic dissociation of electrolytes are surpressed and the ion-pairs predominate in this medium. It was confirmed that AgAgCl electrode gives rise to the Nernstian response in this medium. The potentiometry reveals the formation of following chloro complexes of cobalt (II): Successive formation constants were determined as log K1 = 5.0 ± 0.3, log K2 = 6.2 ± 0.3 (log β2 = log K1K2 = 11.15 ± 0.03) and log K3 = 5.97 ± 0.03. By the spectrophotometric titration at higher concentration of lithium chloride, we have the following equilibrium: with formation constant of log K4 = 2.64 ± 0.05. Absorption spectra of these complexes are presented.