Michel Aplincourt

Bis-aminals: efficient tools for bis-macrocycle synthesis

Tetraazamacrocyclic bis-aminals prove to be excellent tools for the synthesis of symmetrical, dissymmetrical or functionalized bis-tetraazamacrocycles. The key feature of the process is the separation of insoluble mono- or bis-quaternary ammonium salts from solution during the course of the alkylation reaction.

Metal ions binding onto a lignocellulosic substrate extracted from wheat bran: a NICA-Donnan approach

In this study ion binding to solid organic matter was investigated. We used the NICA-Donnan model to describe the interaction between Cu(II), Pb(II), and Cd(II) ions and a lignocellulosic substrate extracted from wheat bran. Such a material represents a very cheap and flexible substrate, which can be used as a natural filter to remove toxic metal ions from industrial effluents or applied in the decontamination and rehabilitation of abandoned industrial sites. Moreover, such a material also represents a very simple model of natural organic matter derived from lignin and cellulose, for which there is now a lack of thermodynamic data as far as their interaction with toxic metal ions is concerned. Experimental results were obtained in various conditions of pH and ionic strength. In our modeling, we used the acidity constants and the concentration of sites that were determined in a previous work. The parameters deduced from the NICA-Donnan model were also compared to thermodynamic data available for other cases of natural organic matter, mainly humic substances.

Characterisation of a wheat straw cell wall residue by various techniques: A comparative study with a synthetic and an extracted lignin

Comparative studies using various analytical and spectroscopic techniques have been carried out on three samples of lignin: two samples of natural lignin that have been extracted using different processes, and one sample of synthetic lignin. This paper discusses the general features common to all three kinds of lignin, as well as the differences between, on one hand, the two natural lignins coming from different extraction processes, and, on the other hand, the natural lignins and the synthetic one. The advantages of each technique in explaining the structure of these three different lignins are emphasised.

Aqueous Chemistry of Zirconium(IV) in Carbonate Media

The interactions between carbonate ions and zirconium oxychloride are studied by potentiometry, dialysis, and 13C- and 17O-NMR spectroscopy in aqueous media. The nature of the soluble carbonatohydroxo complexes depends on the proportions of hydrogencarbonate and carbonate ions in solution before the addition of zirconium oxychloride. Carbonate media lead to polynuclear entities containing no more than two complexed carbonate ions per Zr4+. The presence of hydrogencarbonate favors the formation of less condensed and more carbonated complexes such as [Zr(CO3)4]4−. The polycondensation degree of the species decreases when the number of carbonates linked per Zr4+ increases. In all complexes, the carbonate is bidentate, and the metal atoms are linked via hydroxo bridges. The complexation of carbonate with Zr4+ occurs for a total carbonate concentration higher than 0.1M. Consequently, in natural medium, the speciation of this metal is governed only by the formation of hydroxo complexes.

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.

Iron and manganese surface complex formation with extracted lignin. Part 1: Adsorption isotherm experiments and EPR spectroscopy analysis

The adsorption of iron(III) and manganese(II) onto lignin extracted from wheat straw was investigated at 20 °C using batch adsorption experiments. Two solid substrates were studied : the Ligno-cellulosic Substrate (LS), which resulted from successive acido-basic treatments, and the Cell Wall Residue substrate (CWR), which was obtained by solvent extraction. Comparisons between these two lignin-containing substrates were made. Experiments were conducted as a function of the pH for a wide range of metal concentrations. The percentage of metal adsorbed increased with the pH and the results indicate that Fe(III) was strongly adsorbed at low pH (<3) while Mn(II) formed far less stable surface complexes from pH = 8.0. Moreover, in contrast to Fe(III), Mn(II) adsorption was significantly affected by the presence of calcium and carbonate, which are abundant ions in the soils of the Champagne-Ardenne region. The presence of calcium ions decreased the manganese adsorption by 25% to 40%. EPR spectroscopy was used to investigate the geometrical environment of the metal in the surface complexes. As the metal was adsorbed, redox processes took place, which could be observed by the change in the amount of quinonic species present in the lignin surface. Then, the evolution of quinonic species amount as a function of the metal concentration was examined by EPR measurements considering the signal centred at g = 2.0025. Mechanisms involved in the electronic transfer between the metal ion and the surface organic radicals are discussed.

Speciation of chromium on a straw lignin: adsorption isotherm, EPR, and XAS studies

The binding ability of a lignocellulosic substrate extracted from wheat straw with chromium(III) ion was investigated. The study was carried out at macroscopic and microscopic scales. The adsorbent used was first characterised using X-ray diffraction and electron microscopy. Then, macroscopic studies were conducted using batch adsorption experiments, at room temperature, as a function of time, pH, and metal concentration. The results obtained indicate that several successive phenomena take place at the substrate surface. Indeed, sorption, co-precipitation, and precipitation processes arise depending on the experimental conditions. The speciation of Cr was also investigated, at the atomic scale, by EPR, extended X-ray absorption fine structure (EXAFS), and X-ray absorption near edge structure (XANES). This study revealed that chromium(III) surface complexes have an octahedral geometry. Chromium ions are held in inner-sphere complexes, and are coordinated to six oxygen atoms at an average distance of 1.90 A.

Nickel(II) complexes of cyclen- and cyclam-pyridine: topological reorganisations induced by electron transfer

The NiII complexes of cyclen- and cyclam-pyridine (respectively 1-pyridin-2-ylmethyl-1,4,7,10-tetraazacyclododecane and 1-pyridin-2-ylmethyl-1,4,8,11-tetraazacyclotetradecane denoted [NiIIL1]2+ and [NiIIL2]2+) have been isolated and characterised by X-ray diffraction, UV-visible spectroscopy and electrochemical studies for the [NiIIL2]2+ complex. In particular, the [NiIIL2]2+ complex adopts two distinct and stable geometries (type I and V), which mainly differ by the macrocycle configuration. In solution, the isomerisation process between these two configurations is driven by the nickel-centered electron transfer.

Copper(II) complexes with lactamides: solution and solid state studies

Three functionalized ligands, S(−)-N-(pyridin-2-ylmethyl)lactamide (pml), S(−)-N-(2-dimethylaminoethyl)lactamide (dmael) and S(−)-N-(3-dimethylaminopropyl)lactamide (dmapl), were synthesized by the aminolysis of S(−)-methyl lactate with the corresponding primary amines. Their protonation constants and the stability constants of the chelates formed with copper(II) were determined by potentiometry. In all cases, we detected the formation of CuLH−1+, CuLH−2 and CuLH−3− species (L = free ligand). The copper(II) complexes prepared in the solid state were characterized by IR and UV-visible spectroscopies. The crystal structure of [Cu(pmlH−1)X] (X = Cl, Br) shows that copper(II) is bound to the pyridyl and the deprotonated amidic nitrogen atoms, as well as to the oxygen atom of the hydroxyl group, which leads to a mono-chelated compound. The geometry around Cu2+ is square pyramidal.

Metal cation-ligand interactions of catechols of biological importance—I. Stability of iron(III) dihydroxybenzamide complexes which are related to cephalosporins bearing at C3′ a catechol group

Abstract Iron-chelating properties have been studied with N-ethyl-3,4-dihydroxybenzene-sulphonamide and 5-substituted dihydroxybenzamides as model molecules of β-lactam antibiotics to which are attached similar derivatized catechols. Acidity constants of the model ligands and equilibrium constants of iron(III) complexes have been determined by potentiometry and spectrophotometry at 25°C and 1 mol dm −3 ionic strength (NaClO 4 ). The formation constants show that these ligands form exceptionally stable complexes (log β 3 ⋍ 40) with the ferric ion, which is coordinated through the two phenolic oxygens of the catechol group. No precise correlation between stability constants of Fe 3+ complexes and in vitro microbiological properties has been made. However, it appears that the most potent antibiotics are those bearing substituted catechols possessing the highest chelating properties and lowest p K a 1 values.