New synthesis of a high molecular weight ligand derived from dota; thermodynamic stability of the MRI contrast agent formed with gadolinium.

The new total synthesis in four steps of the compound P1041 is reported. This compound is a high molecular mass ligand (MW 6.32 kDa) derived from dota in which the four substituents are hydroxylated and contain amidic groups. The attribution of the nine protonation constants of P1041 is based on the comparison with the behaviour of the precursor ligands dota and tced, a tetracarboxylated derivative of dota. From these results, the studies of the systems P1041/Na(+) and P1041/Gd(3+) lead to the determination of the stability constants corresponding to the three species Na(P1041)H(h) (h = 0, 2 or 4) and to the five complexes Gd(P1041)H(h) (h = 0, 2, 3, 4 or 5). The complexing ability of P1041 towards Gd(3+) is compared with those of dota and tced. At physiological pH = 7.4, the very stable species Gd(P1041)H(4) (-) (currently named P792 in the literature) of this rapid clearance blood pool agent is predominant.

Use of a low-cost biosorbent to remove pesticides from wastewater.

A lignocellulosic substrate (LS) obtained from our local agroindustry was used as a low-cost and effective adsorbent for the removal of pesticides from wastewaters. The studied pesticides were terbumeton (N-(1,1-dimethyl)-Nethyl-6-methoxy-1,3,5-triazine-2,4-diamine), desethyl terbumeton (N-(1,1-dimethylethyl)-6-methoxy-1,3,5-triazine-2,4-diamine), dimetomorph (4-[3-(4-chlorophenyl)-3-(3,4-dimethoxyphenyl)acryloyl]morpholine), and isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea). Batch and column experiments were conducted as a function of pH and pesticide concentration under laboratory and industrial conditions. The concentration range studied for the pesticides varied from 2 x 10(-7) to 3 x 10(-4) mol L(-1). The influence of organic and inorganic pollutants was assessed by studying the retention of pesticide in the presence of copper(II) and a surfactant. These experiments indicated that LS is an efficient adsorbent toward the investigated pesticides and has little influence of the other pollutants. The kinetic adsorptions are fast, and the amounts of adsorbed pesticide varied from 1 to 8 g kg(-1) of LS. These retention capacities show that LS can provide a simple, effective, and cheap method for removing pesticides from contaminated waters. Thus, this biomaterial may be useful for cleaning up polluted waters.

Thermodynamic and structural properties of Eu3+ complexes of a new 12-membered tetraaza macrocycle containing pyridine and N-glutaryl groups as pendant arms: characterization of three complexing successive phases.

A new polyazamacrocyclic ligand (called pctga) containing pyridine and N-glutaryl arms has been synthesized as a potential agent for MRI (magnetic resonance imaging). Three series of successive complexes formed with Eu(3+) were characterized by at least two of the following methods: potentiometry, EXAFS or luminescence spectrometry. In the immediate complexes [EuH(h)(pctga)(H2O)6](h-3)+**, the metal ion is bound to the oxygen atoms of the three internal carboxylate groups and to six water molecules. As the lanthanide moves into the macrocyclic cavity, these species rapidly evolve into the intermediate metastable complexes [EuH(h)(pctga)(H2O)4](h-3)+*. The formation of two new bonds with the nitrogen atoms of the tetraazamacrocycle decreased the number of coordinated water molecules to four. In the final thermodynamically stable complexes [EuH(h)(pctga)(H2O)(2)](h-3)+, the pctga is bound to the europium(III) in a heptadentate manner, via the four nitrogen atoms of the tetraazamacrocycle and the three oxygen atoms of the internal carboxylate groups. The coordination number of the metal ion is completed to nine with two inner-sphere water molecules. The mean hydration numbers were calculated from the values of the bimolecular quenching constant k(q) of the luminescence species. The thermodynamic parameters corresponding to the protonation constants of the ligand and to the formation constants of the various intermediate and final complexes were determined from potentiometric measurements. They show that the complex species have some specific thermodynamic and structural properties inherent to the N-glutaryl groups and to the pyridine cycle. The insertion of this aromatic substructure rigidifies the ligand and sensibly diminishes the value of the overall formation constant (log beta(110) = 18.66(5)). This whole study allows us to propose a complexation mechanism for the system Eu(3+)/pctga in solution which is a mixture of the ones determined for the ligands dota and tced.

Sorption of Cu(II) onto vineyard soils: macroscopic and spectroscopic investigations.

The sorption of Cu on five vineyard soils was examined via macroscopic and spectroscopic investigations. The composition of the soils was previously determined using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). X-ray absorption spectroscopy (XAS) was employed to determine the metal environment with regard to the identity and interaction of the nearest atomic neighbors, the bond distances, and the coordination numbers. The five soils present similar sorption properties and there is no XAS evidence that the nature of the soil samples affects the local chemical environment of Cu(II). The kinetics of the Cu sorption reactions is rapid, with the equilibrium loading of Cu on the surface achieving approximately 200 mumol g(-1), i.e., 12.7 mg g(-1). The XAS data indicate that Cu is adsorbed in the form of inner-sphere complexes with first shell CuO parameters of four equatorial CuO bonds equal to 1.93 A and two axial CuO bonds at 2.43 A. This is in accordance with a Jahn-Teller distorted octahedron environment around copper. Our results provide evidence of the complexation of Cu(II) onto soil organic matter coated with an inorganic surface (quartz, clay, and goethite).

Thermodynamic and spectroscopic studies of copper (II) complexes with three bis(amide) ligands derived from L-tartaric acid.

The interactions of three bis(amide) ligands derived from tartaric acid with copper (II) were investigated in aqueous solution by a combination of potentiometry, UV-vis spectrophotometry, electron paramagnetic resonance (EPR), and mass spectrometry. The formation constants of the complexes were measured and their relative structures were reported. The sites of complexation of these ligands are investigated based mostly on their electronic and EPR spectra and on the comparison with the behaviour of some analog compounds.

Adsorption of several metal ions onto a model soil sample: equilibrium and EPR studies.

Soils play an important role in the control of metallic cations in the environment. Therefore, knowledge of the adsorption properties of soil is crucial in understanding and solving pollution problems. Adsorption isotherms provide a macroscopic view of the retention phenomena. The aim of this paper is to study iron, manganese, and chromium adsorption onto a soil sample as a function of the reaction time, pH, and metal concentration. The adsorption isotherms allow the determination of the affinity order of metals for the surface of the soil sample as such: Fe(3+)>Cr(3+)>Mn(2+). The equilibrium data fit well with the Langmuir and Freundlich models and confirm the affinity order of the soil sample for these metals. These adsorption data are combined with EPR spectroscopy to obtain structural information about the surface complexes formed. Iron is held in inner-sphere complexes. Manganese is simultaneously held in outer- and inner-sphere complexes. Due to poor resolution, chromium was not detected by EPR and thus it is impossible to infer coordination sphere and coordination number. Iron and manganese are in an octahedral environment.

Use of analytical microscopy to analyze the speciation of copper and chromium ions onto a low-cost biomaterial.

In this paper, we present our study of the speciation of copper and hexavalent chromium sorbed onto a lignocellulosic substrate, using analytical microscopy. The lignocellulosic substrate constitutes a low-cost biomaterial that can be used in wastewater treatment. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) was used to determine the speciation of the two metal ions on the constitutive moieties of the lignocellulosic substrate. The use of a staining agent sensitive to carbon unsaturation allowed us to differentiate between the microstructures rich in lignin entities and those rich in cellulose entities. The EDX analysis showed that metal ions are preferentially sorbed onto microstructures rich in lignin moieties. The energy electron loss spectroscopy (EELS) was used to determine the oxidation states of chromium in association with lignocellulosic moieties. We showed that the sorption process of hexavalent chromium requires the reduction of Cr(VI) into Cr(III) and the probable oxidation of lignin moieties.

Complexing mechanism of the lanthanide cations Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota)-characterization of three successive complexing phases: study of the thermodynamic and structural properties of the complexes by potentiometry, luminescence spectroscopy, and EXAFS.

Complexation of the lanthanides Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota) has been studied in solution by using potentiometry, luminescence spectrometry, and EXAFS. Three series of successive complexes were characterized by at least two of these methods: the immediate [LnHn(dota)](n-1)+** and intermediate [LnHn(dota)](n-1)+* complexes with 0

Surface complexation of copper(II) on soil particles: EPR and XAFS studies.

The interactions of transition metals with natural systems play an important role in the mobility and the bioavailability of these metals in soils. In this study, the adsorption of copper(II) onto natural soil particles was studied as a function of pH and metal concentration. The retention capacity of soil particles was determined at pH 6.2 to be equal to 6.7 mg of copper/g of solid. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior of the system at different pH values. A combination of EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near-edge structure (XANES) spectroscopies was used to probe the Cu atomic environment at the soil particles/aqueous interface. The spectroscopic study revealed that copper(II) ions are held in inner-sphere surface complexes. It also revealed that Cu was in an octahedral coordination with first-shell oxygen atoms. A weak tetragonal distortion was pointed out due to the Jahn-Teller effect, with a mean Cu-Oequatorial bond distance of 1.96 A and a Cu-Oaxial bond distance of 2.06 A. A detailed analysis of the spectroscopic data suggested that Cu(II) was bonded to organic matter coated onto the mineral fraction of soil particles.

Molecular scale speciation of first-row transition elements bound to ligneous material by using X-ray absorption spectroscopy.

To develop a solid scientific basis for maintaining soil quality and formulating effective remediation strategies, it is critical to determine how environmentally-important trace metals are sequestered in soils at the molecular scale. The speciation of Mn, Fe and Cu in soil organic matter has been determined by synchrotron-based techniques: extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES). We show the structural similarity between the surface complexes of Mn(II), Fe(III) and Cu(II). These cations are bound to the surface through oxygen atoms. Each one presents a more or less tetragonal-distorted octahedral geometry. The use of X-ray absorption spectroscopy provides a relevant method for determining trace-metal speciation in both natural and contaminated environmental materials.

Spectroscopic study of copper(II)--wheat straw cell wall residue surface complexes.

The sorption of copper(II) by wheat straw cell wall residue (CWR) was studied and revealed a relatively stable surface complexation on the acid sites of the substrate (carboxylic and phenolic moieties). The copper binding capacity at pH = 5.75 and ionic strength of 0.1 M was evaluated at 63 micromol x g(-1) CWR. The Langmuir and Freundlich isotherm equations were then used to describe the partitioning behavior for the system at different pH values. Batch experiments have been achieved in the presence of calcium in order to mimic the calcareous soil of the Champagne region. A competitive effect on copper complexation has been shown, which is presumably due to the calcium ability to form outer-sphere complexes far less stable than copper(II) ones. Electron spin resonance and X-ray absorption spectroscopy were combined to obtain information on the geometry and structure of Cu bound to CWR. At least two different binding sites for Cu2+ were found to take place in CWR. From ESR parameters, we deduced that copper(II) ions, when complexed with CWR, are coordinated in a square-planar arrangement with four oxygen-containing groups. EXAFS and XANES experiments revealed that Cu(II) is surrounded by four oxygen atoms, with an average Cu-O equatorial distance equal to 1.94 A.

Experimental study and modelling of lead solubility as a function of pH in mixtures of ground waters and cement waters.

The purpose of this study was the simulation of lead solubility equilibria in mixtures of concrete lixiviation waters and ground waters in order to obtain the data necessary for the modelling of lead behaviour. The lixiviation water was impossible to obtain in sufficient quantity by compression of concrete specimens and was replaced by cement water prepared by mixing a CLC or CPA cement suspension in distilled water under argon. Three lead salts, PbCl2, PbSO4 and PbCO3, were studied; they correspond to the anions found most frequently in the ground waters. The experimental curves of lead solubility were determined, at 20 degrees C, from pH 5 to 13, for various systems: cement water/lead salt/ground water. The modelling of 10 systems was carried out by the PHREEQC code from the solution compositions (ground water and cement water mixtures) and the thermodynamic constants obtained from the MINTEQ data base. The chemical models included the nature of the species in solution and the solid phases in equilibrium together with the corresponding values for the logarithms of the formation constants or solubility products. These models were validated by comparing the experimental pH and solubilised lead concentration values with the values calculated using the PHREEQC code.

EXAFS and XANES studies of retention of copper and lead by a lignocellulosic biomaterial.

Lignocellulosic substrate (LS), which is a low cost biomaterial, has a strong complexing ability and can be used in the treatment of wastewaters as biosorbentto remove heavy metals. The speciation of copper and lead to this biomaterial has been studied by X-ray absorption spectroscopy. The copper(II) has a 6-coordinate structure with four oxygen atoms in the equatorial plane at 1.95 A and two in axial position at 2.35 A. In the case of lead a particularly low coordination number of about 3 has been obtained. The combination of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) suggested that Cu and Pb are bound to the surface of LS through carboxylic moieties.

Copper sorption on a straw lignin: experiments and EPR characterization.

Spectroscopic and physicochemical data, X-ray photoelectron spectroscopy (XPS), solid-state (13)C cross-polarization magic-angle-spinning NMR, GC/MS, specific surface area, site density, and surface acidity constants have been recorded or determined for a ligno-cellulosic substrate (LS) extracted from straw. Its copper(II)-bound ability has also been studied. The LS solid that exhibits two types of binding sites, carboxylic and phenolic groups, has a great affinity for copper(II), with a maximum of adsorption at around 4 mg g(-1) as early as the pH reaches 6. The structural characterization of the Cu(II) surface complexes has been investigated using EPR spectroscopy. The CuO(4) chromophore of the inner-sphere surface complexes is a slightly distorted square. A surface oxidation occurred simultaneously, which leads to semiquinonic radicals. Furthermore, our empirical approach, which used a correlation between thermodynamics data and EPR parameters, has led to a surface complexation constant log beta equal to 12.6. This indicates that copper(II) surface complexes are relatively stable.

Structural Characterization and Iron(III) Binding Ability of Dimeric and Polymeric Lignin Models.

To understand the complexation in solution and the sorption of iron(III) on soluble and solid fractions of lignin, a dimeric model (guaiacyl-beta-guaiacylglycerol ether, called beta-O-4) and a polymeric model (dehydrogenation polymer resulting from polymerization of coniferyl alcohol) of lignin have been synthesized and characterized with chromatographic, solution, and solid state (13)C CP-MAS NMR and XPS spectroscopies. The beta-O-4 dimer is a monoacid (HL). Potentiometric studies in aqueous solution at 25 degrees C and 1 mol L(-1) ionic strength (KNO(3)) indicated formation of two stable complexes, FeL(2+) and probably FeL(OH)(+), which shows that the soluble fraction of lignin binds metals, indicating that they are transported by water through the soils. The binding of iron(III) on the DHP polymer was then investigated. The sorption experiments have shown a great affinity of iron for the solid with a maximum of adsorption since pH 5. A pulsed-ESR study has revealed surface oxidation by the iron(III) cation, which leads to iron(II) and semiquinonic radicals on the polymer surface, with a radical concentration of about 5x10(17) spin/g. Copyright 2001 Academic Press.