Search

International audience; Scaling process is the main problem encountered in industrial plants using water. Several factors, (pH, temperature, hydrodynamic conditions, metal surface, and especially, water composition),can affect the scaling kinetics of calcium carbonate (CaCO3), one of the main component of scaling. In addition, some foreign ions added can considerably modified the scaling rates. In thiswork, the inhibiting effects of Zn2+ and Cu2+ cations on CaCO3 precipitation were studied in a 50°F synthetic carbonic solution by using fast controlled precipitation (FCP) and scaling quartz crystal microbalance (SQCM) methods, for homogeneous and heterogeneous scaling deposition, respectively. Results showed that Zn2+ and Cu2+ ions are efficient, at high concentrations (≥ 1mg/L), to delay or even to prevent nucleation/growth of CaCO3. FCP measurements showed a complete inhibition of the homogeneous CaCO3 precipitation after 120 min in synthetic solutioncontaining 5 mg/L and 4 mg/L of Cu2+ and Zn2+, respectively. SQCM measurements showed that the surface coverage of the metallic substrate by a layer of CaCO3 is reduced when the amount of these cations increased. Zn2+ cations inhibited the heterogeneous CaCO3 precipitation moree fficiently than Cu2+. SEM and XRD results indicated that both cations affect calcium carbonatenucleation by changing the morphology of CaCO3 crystals

International audience; Scale deposition is a common issue in industrial plants, which creates technical problems, i.e. reduction of heat transfer, decrease of flow rate due to an obstruction of pipes. Therefore, the development of some appropriate methods based on well suitable in situ sensors to evaluate and predict the scaling propensity of water is a major concern in current research. This would be a good strategy for the optimization of anti-scaling treatments.In this study, scaling tests were carried out using a sensitive sensor, which has been developed using a quartz crystal microbalance with a pre-calcified electrode surface (SQCM). This technique allowed studying the influence of the supersaturation on the scaling rate. The set-up was tested with different water samples which were brought to a given supersaturation coefficient by degassing the dissolved CO2. The prediction of the scaling propensity of water was then possible through the relationship between the scaling rate on a pre-calcified surface and the supersaturation coefficient. In addition, the kinetics of CaCO3 deposit on the pre-calcified SQCM surface was found to be slower for natural water than for synthetic water (same calcium concentration). Furthermore, the activation energy for scale deposit, in synthetic water, was found to be 22 kJ.mol−1, which may be related to the diffusion of ions and/or CaCO3 nuclei in solution.

International audience; The formation of calcium carbonate in water has important implications in industry. Chemical antiscalant is usually used to control scale depositions. Plant extracts have been recently used as new green antiscalant agents, as they can be easily prepared and are environmentally friendly. In this study, stock aqueous solutions of Spergularia rubra and Parietaria officinalis, two plants used in traditional medicine to treat or prevent urolithiasis, were obtained by infusion. The antiscaling properties of these extracts towards CaCO3 formation were tested by using chronoamperometry and Fast Controlled Precipitation methods. The aqueous solution of S. rubra was further fractionated to isolate compounds of lower polarity. Their efficiency towards CaCO3 precipitation was characterized by Fast Controlled Precipitation method. The inhibiting efficiency of this fractionated solution was greater than that of the stock aqueous solution.

International audience; The formation of calcium carbonate in water has some important implications in geoscience researches, oceanchemistry studies, CO2 emission issues and biology. In industry, the scaling phenomenon may cause technicalproblems such as reduction of heat transfer efficiency in cooling systems and obstruction of pipes.The use of chemicalswhich act as antiscalant is a common approach in the control of scale deposition. However,inorganic nitrogen and phosphorous compounds are involved in eutrophication process. Therefore, it is of primeimportance to find alternative solutions, i.e. green inhibitors of scale formation. This last decade, several newscaleinhibitors, that are more ecological compared with conventional inhibitors, have been reported in the literature.Plant extracts have been also recently used as newgreen antiscalants. Indeed, as they can be easily extracted andare environmentally friendly, they represent an interesting alternative source of "natural" organic molecules.In this review, a focus of some green antiscalants derived frompetrochemicals has been reported. Then the effortsdone those last years to obtain green inhibitors, either by using “natural” organic molecules or extracted fromplants were summarized. Such green inhibitors might be used in various technical areas, i.e. energy, water,food and beverages industries.

In this paper, the inhibiting properties of an aqueous solution containing Hylocereus undatus towards CaCO 3 formation were studied by using fast controlled precipitation and chronoamperometric methods, in order to study the calcium carbonate formation in solution and on a metallic surface, respectively. As a purpose of comparison, the antiscaling properties of citric acid were studied in the same experimental conditions. The results obtained by fast controlled precipitation method showed that Hylocereus undatus solution was more efficient than citric acid to inhibit CaCO 3 formation in solution (optimal concentrations of 20 and 24 mg.L –1 , respectively). By using the chronoamperometric method, a concentration of citric acid at 160 mg.L -1 was required to totally prevent the precipitation of CaCO 3 whereas it was 180 mg.L -1 for Hylocereus undatus solution. The morphology analysis by scanning electronic microscopy and X-ray diffraction revealed that vaterite was favored in the presence of Hylocereus undatus solution, whereas a mixture of calcite and vaterite was obtained with citric acid.

International audience; Chemical antiscalants are usually used to control scale depositions, a major concern in industry. Some of these products may be harmful towards environment or toxic for humans, so environmentally friendly antiscalant are needed. In this respect, plant extracts can be used as new green antiscalant agents. In this work, stock aqueous solution of Herniaria glabra (H. glabra) was obtained by infusion. H. glabra is used in traditional medicine to treat or prevent urolithiasis; it could be an interesting candidate as a green antiscaling agent. The properties of H. glabra towards CaCO3 formation were tested by using chronoamperometry and Fast Controlled Precipitation methods. An n-butanol solution was used to partition the aqueous solution of H. glabra, yielding a polar compounds-free fraction. This fraction was also studied by chronoamperometry and Fast Controlled Precipitation methods. The results showed a better inhibition efficiency towards CaCO3 precipitation for the n-butanol fraction compared to the crude H. glabra solution.

In this work, the nature of the deposit found inside an industrial cooling circuit (which consists of a mixture of different iron containing phases) has been characterized in detail by 57Fe Mossbauer spectroscopy. Electron Paramagnetic Resonance spectroscopy was also used to check for the presence of other metals, mainly manganese and copper, detected by the Inductive Coupled Plasma method. We conclude that the deposit contains a large amount of Fe(III), probably consisiting of ferrihydrite nanoparticles and of goethite, either bulk or as large particles. It also contains traces of an Fe(II) species (about 3%), probably adsorbed on the iron oxides. Mn(II) and traces of Cu(II) are also present.

An organophosphorous ligand terminated by an amine group has been used here for the first time to functionalize γ-Fe 2 O 3 nanoparticles and to immobilize an enzyme onto their surface in a covalent way. The immobilization of β-glucosidase onto the maghemite nanoparticles was carried in this work out via a reductive amination reaction pathway which involves the terminal amine group on the ligand. The enzymatic activity of the bound enzyme was evaluated in terms of the classical Michaelis–Menten kinetics. Indeed, the affinity of the bound enzyme for the substrate is preserved and is not affected by the high amount of enzymes onto the surface of the nanoparticles. Moreover, the related enzymatic activity slightly decreases compared to that of the free enzyme. Such functionalized nanoparticles could help to improve the delivery and the recovery of biomolecules in biomedical applications by using a magnetic field. They could also provide a magnetic support which could be involved as a contrast agent, a biological label and a mediator for magnetic hyperthermia.

International audience; In this paper, the inhibition efficiency of two inhibitors, namely poly(acrylic acid-co-maleic acid) and polyaspartic acid, towards calcium carbonate scaling was evaluated using fast controlled precipitation (FCP) method and electrochemical quartz crystal microbalance (EQCM). FCP method gave some insight to the calcium carbonate precipitation in solution, whereas EQCM was used to study the calcium carbonate formation on a metallic substrate. It has been shown that these polymers were efficient to delay or to prevent nucleation/growth process, depending on their concentration. Moreover they significantly decreased the crystal growth rate. The FCP method showed that these inhibitors were very efficient at low concentrations (4 mg L−1) when no precipitation occurred. In addition, EQCM showed that the surface coverage of deposits on a substrate was reduced by the presence of these inhibitors at very low concentration (4 mg L−1). Scanning electronic microscopy and X-ray diffraction showed that the presence of these polymers modified the morphology of calcium carbonate crystal. In order to model nucleation/growth process of calcium carbonate on surface, mass–time transients were interpreted using a 3D model based on a nucleation following a Poisson law associated to vertical and lateral growth rates.

International audience; The tetrapodal pentaamine 2,6-C5H3N[CMe(CH2NH2)2]2 (pyN4, 1), which possesses four equivalent primary amino groups, has been used to prepare the diiron(III) oxo complex [(1)2Fe2(μ2-O)](ClO4)4(2), by aerobic oxidation of the mononuclear iron(II) aqua complex in methanol. This synthesis is unusual because iron(II) complexes of primary amines are normally unstable with respect to metal-induced ligand oxidation. X-ray as well as Mössbauer data indicate a high-spin electronic configuration for the metal centres in the dinuclear complex.

A small magnetic field, applied either parallel or perpendicular to the direction of Mossbauer γ-rays, is produced on an absorber by two Mossbauer sample-holders. The sample-holders constitute a convenient and affordable way to obtain the experimental conditions necessary for interpreting the paramagnetic Mossbauer spectra of Kramers iron systems. An application of the two sample-holders is illustrated by the study of a high-spin Fe(III) complex (S = 5/2).

The purple hydrogenperoxo species [Fe(bztpen)(OOH)]2+ (1) can be generated in methanol solution by treatment of [Fe(bztpen)Cl]3+ with a large excess of hydrogen peroxide [A. Hazell, C. J. McKenzie, L. P. Nielsen, S. Schindler, M. Weitzer, J. Chem. Soc., Dalton Trans.2002, 310−317]. Addition of 30 equivalents of triethylamine to a solution of [Fe(bztpen)(OOH)]2+ gives the [Fe(bztpen)(O2)]+ (2) species, in which it has been proposed that the peroxo ligand is coordinated in the η2 mode. We have synthesized both 100% 57Fe-enriched non-heme FeIII peroxo species and studied them by EPR and Mossbauer spectroscopy. Species 1 displays a typical S = 1/2 low-spin ferric EPR spectrum, the g values of which have been analysed in terms of the Griffith model [J. S. Griffith, Proc. R. Soc. London, A1956, 234, 23−36]. We have thus obtained insight into the electronic structure of 1. The EPR spectrum of 2 is characteristic of a high-spin FeIII species in a nearly axial ligand field. We have determined all Mossbauer parameters for both complexes by a numerical treatment of applied field Mossbauer data. Species 1 exhibits an isomer shift δ/Fe = 0.16 mm/s and a quadrupole splitting ΔEQ = −2.08 mm/s (T = 4.2 K). In the case of 2, we obtain an isomer shift δ/Fe = 0.63 mm/s and a quadrupole splitting ΔEQ = 1.12 mm/s (T = 4.2 K). These values are close to those published very recently by Bill et al. for [Fe(trispicMeen)(OOH)]2+ (3) and [Fe(trispicMeen)(η2−OO)]+ (4) species, where bztpen and trispicMeen ligands differ by a noncoordinating group [A. J. Simaan, F. Banse, J.-J. Girerd, K. Wieghardt, E. Bill, Inorg. Chem.2001, 40, 6538−6540]. We have also used the extension of the Griffith model developed by Lang et al. for Mossbauer spectroscopy [W. T. Oosterhuis, G. Lang, Phys. Rev. 1969, 178, 439−456] to evaluate the 57Fe hyperfine tensor of 1 and reproduce the experimental data. On comparison with the Mossbauer data available for η2-peroxo FeIII complexes, our Mossbauer study of 2 agrees well with a high-spin FeIII side-on peroxo complex. Very characteristic δ/Fe and ΔEQ ranges for hydrogenperoxo and side-on peroxo FeIII species are now available, which should aid in the detection of comparable species formed in biological systems. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

An isotopically enriched [57Fe(edta)(O2)]3− complex, formed by the addition of H2O2 to a 57FeIII-edta (edta = ethylenediaminetetraacetic acid) complex at elevated pH (pH = 11.3), was studied by Mossbauer spectroscopy. All Mossbauer parameters were determined for this nonheme high-spin ferric peroxo complex with an η2-FeO2 (side-on) arrangement by a numerical treatment of applied field Mossbauer data. The peroxo complex exhibits an isomer shift δ/Fe = 0.65(1) mm s−1 and a quadrupole splitting ΔEQ = +0.72(2) mm s−1 (T = 4.2 K). The isomer-shift value is very similar to the value of δ/Fe = 0.61 mm s−1 published for the side-on peroxo complex [FeIII(N4Py)(η2-OO)]+ (Py = pyridine) [V. Vrajmasu, E. Munck, R. Ho, L. Que, Jr., G. Roefles, B. L. Feringa, J. Inorg. Biochem.2001, 86, 472]. The set of Mossbauer parameters obtained herein is expected to aid the characterization of analogous species that may appear during dioxygen activation by nonheme mononuclear iron enzymes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

International audience; The initial stage of calcium carbonate nucleation and growth, found usually in "natural" precipitation conditions, is still not well understood. The calcium carbonate formation for moderate supersaturation level could be achieved by an original method called the fast controlled precipitation (FCP) method. FCP was coupled with SAXS (small-angle X-ray scattering) measurements to get insight into the nucleation and growth mechanisms of calcium carbonate particles in Ca(HCO3)2 aqueous solutions. Two size distributions of particles were observed. The particle size evolutions of these two distributions were obtained by analyzing the SAXS data. A nice agreement was obtained between the total volume fractions of CaCO3 obtained by SAXS analysis and by pH-resistivity curve modeling (from FCP tests).

The new disymmetric ligand N,N,N′ -tris(2-pyridylmethyl)- N′ -(2-salicylideneethyl)ethane-1,2-diamine (LH) has been synthesized in the search of a novel type of manganese complex to mimic the active site of the water-oxidizing enzyme in photosystem II. The complex [Mn(II)L]ClO 4 has been obtained and characterized by X-ray diffraction techniques. It crystallizes in the monoclinic space group Pn with the following unit cell parameters: a =10.164(3), b =10.122(4), c =14.166(5) A, β =93.48(2)° and Z =2. The manganese ion is heptacoordinated with the coordination being achieved by only one ligand; it is bonded to the oxygen atom of the phenolate group in an axial position, the imino and the three pyridine nitrogen atoms in an equatorial position and the two amine atoms in a pseudo-axial position. The coordination polyhedron is best described as a distorted monocapped trigonal prism. This structure was compared with the seven-coordinated Mn(II) complexes deposited in the Cambridge Structured Database (CSD). The redox potential of the Mn(III)/Mn(II) couple was determined by cyclic voltammetry.

In plants, solar energy is used to extract electrons from water, producing atmospheric oxygen. This is conducted by Photosystem II, where a redox ”triad” consisting of chlorophyll, a tyrosine, and a manganese cluster, governs an essential part of the process. Photooxidation of the chlorophylls produces electron transfer from the tyrosine, which forms a radical. The radical and the manganese cluster together extract electrons from water, providing the biosphere with an unlimited electron source. As a partial model for this system we constructed a ruthenium(II) complex with a covalently attached tyrosine, where the photooxidized ruthenium was rereduced by the tyrosine. In this study we show that the tyrosyl radical, which gives a transient EPR signal under illumination, can oxidize a manganese complex. The dinuclear manganese complex, which initially is in the Mn(III)/(III) state, is oxidized by the photogenerated tyrosyl radical to the Mn(III)/(IV) state. The redox potentials in our system are comparable t...

The Mn4 complex which is involved in water oxidation in photosystem II is known to exhibit three types of EPR signals in the S2 state, one of the five redox states of the enzyme cycle: a multiline signal (spin 1/2), signals at g > 5 (spin 5/2), and a signal at g = 4.1 (spin value 3/2 or 5/2). The multiline and g = 4.1 signals are those the most readily observed. The relative proportions of the g = 4.1 signal and of the multiline signal are affected by many biochemical treatments including the substitution of Ca2+and Cl- which are two essential cofactors for O2 evolution. The state responsible for the multiline signal can also be converted, reversibly, to that responsible for the g = 4.1 signal upon the absorption of near-IR light at around 150 K. These infrared-induced effects are confined to the Mn4 cluster, and no other redox change occurs in the enzyme. Here, we have used the IR-induced photochemistry of the Mn4 cluster to measure the changes in magnetization occurring upon interconversion of the stat...

The synthesis and structural characterization of the novel [MnIII,IV2O2(N,Nbispicen)2](ClO4)3·CH3CN complex employing the tetradentate ligand N,Nbispicen = N,N-bis(2-pyridylmethyl)-1,2-diaminoethane are reported. Magnetic properties were determined and show that the ground state is a spin doublet. This can be quantitatively interpreted by antiferromagnetic coupling between a Mn(III) high spin and a Mn(IV) (J = −316 cm−1). The 16 line solution EPR spectrum exhibits an unusual splitting in the low field resonances. The following rhombic tensors were needed to simulate the EPR spectrum: |A1x|= 160 10−4 cm−1, |A1y| = 144 10−4 cm−1, |A1z|= 109 10−4 cm−1, |A2x|= 69 10−4 cm−1, |A2y| = 72 10−4 cm−1, |A2z| = 75 10−4 cm−1, gx = 2.001, gy = 1.996, gz = 1.984. The classical ligand field theory of local [gIII] and [gIV] tensors implemented with the first order perturbation theory to describe the properties of the pair does not result in a satisfying description of the [g1/2] tensor unless a large reduction in the spin-orbit constant is invoked. A simplified version of second-order perturbation theory leads to effects in qualitative agreement with experiment but weak as expected from the large |J| value. The magnitude of these effects depends, however, on the anisotropy effects on each Mn ion. It is suggested that determination of the anisotropy of the magnetic properties of the monomeric Mn(III) and Mn(IV) moieties would be a valuable goal for a future study of these mixed valent dimanganese-di-μ-oxo complexes. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, one at E1/2 = 0.18 V vs SCE for the III/IV █ III/III couple and the other at E1/2 = 0.98 V vs SCE for the III/IV █ IV/IV couple. The UV-Vis spectra of the three redox states have been recorded spectroelectrochemically.

International audience; The Proteus mirabilis catalase is one of the most efficient heme-containing catalase and forms a relatively stable compound II. Samples of compound II were prepared from PMC enriched in 57Fe. For the first time, two different forms of compound II, namely low pH compound II (LpH II) (43%) and high pH compound II (HpH II) (25%), have been characterized by Mössbauer spectroscopy at pH 8.3. The ratio LpH II/HpH II increases irreversibly with decreasing pH. The large quadrupole splitting value of LpH II (ΔEQ = 2.29 (2) mm/s, with δ/Fe = 0.03 (2) mm/s), compared to that of HpH II (ΔEQ = 1.47 (2) mm/s, with δ/Fe = 0.07 (2) mm/s), reflects the protonation of the ferryl group. Quadrupole splitting values of 1.46 and 2.15 mm/s have been computed by DFT for optimized models of the ferryl compound II (model 1) and the protonated ferryl compound II (model 2), respectively, starting from the FeIVO model initially published by Rovira and Fita [C. Rovira, I. Fita, J. Phys. Chem. B 107 (2003) 5300–5305]. Therefore, we attribute the LpH II compound to a protonated ferryl FeIV–OH complex, whereas the HpH II compound corresponds to the classical ferryl FeIVO complex.

International audience; In an industrial cooling circuit supplied with raw river water, the scaling phenomena can reduce cooling efficiency and even lead to the shutdown of the power plant. During the last twenty years, various methods have been developed in order to estimate the scaling propensity of natural waters, which involve the precipitation of calcium carbonate (CaCO3), the main component of scale. The Fast Controlled Precipitation (FCP) is a non-electrochemical method which consists in CO2 degassing from water by a moderated agitation. FCP allows quantifying the scaling propensity for natural water. It could be a useful tool in order to prevent the scaling risk in industrial installations. In this study, efforts have been made in order to make the FCP method controllable and reliable. For the first time, FCP was applied to raw water (raw river from the Seine River) during a long period of time. It gave some insights on the scaling propensity of the Seine water, depending on the water quality and on the season. The FCP method also appeared to be very sensitive. It could be used to assess the efficiency of a humic acid treatment towards scaling. This work showed that natural compounds such as humic acids contained in river waters could have, at low concentration, a great impact on their scaling propensity.

The synthesis and structural characterization of the novel [MnIII,IV2O2(N,Nbispicen)2](ClO4)3·CH3CN complex employing the tetradentate ligand N,Nbispicen = N,N-bis(2-pyridylmethyl)-1,2-diaminoethane are reported. Magnetic properties were determined and show that the ground state is a spin doublet. This can be quantitatively interpreted by antiferromagnetic coupling between a Mn(III) high spin and a Mn(IV) (J = −316 cm−1). The 16 line solution EPR spectrum exhibits an unusual splitting in the low field resonances. The following rhombic tensors were needed to simulate the EPR spectrum: |A1x|= 160 10−4 cm−1, |A1y| = 144 10−4 cm−1, |A1z|= 109 10−4 cm−1, |A2x|= 69 10−4 cm−1, |A2y| = 72 10−4 cm−1, |A2z| = 75 10−4 cm−1, gx = 2.001, gy = 1.996, gz = 1.984. The classical ligand field theory of local [gIII] and [gIV] tensors implemented with the first order perturbation theory to describe the properties of the pair does not result in a satisfying description of the [g1/2] tensor unless a large reduction in the spin-orbit constant is invoked. A simplified version of second-order perturbation theory leads to effects in qualitative agreement with experiment but weak as expected from the large |J| value. The magnitude of these effects depends, however, on the anisotropy effects on each Mn ion. It is suggested that determination of the anisotropy of the magnetic properties of the monomeric Mn(III) and Mn(IV) moieties would be a valuable goal for a future study of these mixed valent dimanganese-di-μ-oxo complexes. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, one at E1/2 = 0.18 V vs SCE for the III/IV █ III/III couple and the other at E1/2 = 0.98 V vs SCE for the III/IV █ IV/IV couple. The UV-Vis spectra of the three redox states have been recorded spectroelectrochemically.

The Fe2+ center of iron-substituted ferric uptake regulation protein (Fur) has been fully characterized by applied-field Mossbauer spectroscopy, and two structural models for this center in Fur from E. coli (EC-Fe2+Fur) have been developed by combining the crystallographic data available for Fur from Pseudomonas aeruginosa (PA-Fur) in complex with Zn2+ and the EXAFS data for a PA-Fur sample dialyzed against a Fe2+ solution or EC-Fur in complex with Fe2+. The Mossbauer (isomer shift excluded) and spin-Hamiltonian parameters have been estimated by density functional calculations for these models and compared to the experimental data. The geometry and the environment of the iron-binding center in EC-Fur and PA-Fur are found to be similar, and the comparison of the observed and calculated quadrupole splitting values indicates that the model with a (3O,2N,1O) coordination (ΔEQ > 0) is a better representation of the environment around the iron center in EC-Fe2+Fur.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) The article “Detailed Mossbauer Characterization of Fe2+Fur, the Active Form of the Ferric Uptake Regulation Protein from E. coli and Density Functional Calculations on Some Related Models” by Olivier Horner, Jean-Louis Oddou, Claudine Jeandey, Isabelle Michaud-Soret, Jean-Marie Mouesca, published online on June 3, 2009 in Wiley Interscience (www.interscience.wiley.com, 10.1002/ejic.200900091) and in print (Eur. J. Inorg. Chem.2009, 2959–2966), has been retracted (October 6, 2009) by the journal editor-in-chief, Dr Karen Hindson, and Wiley-VCH, in accordance with the “EUCheMS Ethical Guidelines for Publication in Journals and Reviews” adhered to by the journal (EUCheMS Ethical Guidelines for Publication in Journals and Reviews, 2006, http://www.euchems.org/Publications/index.asp), due to lack of agreement among the authors regarding its publication.

The preparation of core-shell-shell γ-Fe2O3/SiO2/TiO2 nanoparticles of few tens nanometers is performed by successively coating onto magnetic nanoparticles a SiO2 layer and a TiO2 layer, using sol–gel methods. The thickness of the two layers and the aggregation state of the particles can be controlled by the experimental conditions used for the two coatings. These composite nanoparticles may find application as magnetic photocatalysts, since they are characterized by their small diameters which allow a good accessibility to the TiO2 shell.

By combining magnetic properties with nanosized biocompatible materials, superparamagnetic nanoparticles may serve as colloidal heating mediators for cancer therapy. This unique potential has attracted attention for designing new magnetic nanoparticles with high efficiency heating properties. Their heating power under high frequency magnetic field is governed by the mechanisms of magnetic energy dissipation for single-domain particles due both to internal Néel fluctuations of the particle magnetic moment and to the external Brownian fluctuations. These mechanisms are highly sensitive to the crystal size, the particle material, and the solvent properties. Here we explore the heating properties of maghemite particles with large particle sizes, in the range 15-50 nm, synthesized through a new procedure which includes a hydrothermal process. Particle shape and size distribution, hydrodynamic volume, and magnetic anisotropy are characterized, respectively, by transmission electron microscopy, dynamic magnetically induced birefringence, and ferromagnetic resonance. Together with our previous data on low diameter particles (Fortin J P et al 2007 J. Am. Chem. Soc 129 2628-35), this study provides the whole size dependence of heating efficiency in the range 5-50 nm and assesses the balance between Néel and Brownian contributions to thermal losses. In agreement with theoretical predictions, the heating efficiency shows a maximum for an optimal size of about 15 nm.

The catalase from Proteus mirabilis peroxide-resistant bacteria is one of the most efficient heme-containing catalases. It forms a relatively stable compound II. We were able to prepare samples of compound II from P. mirabilis catalase enriched in (57)Fe and to study them by spectroscopic methods. Two different forms of compound II, namely, low-pH compound II (LpH II) and high-pH compound II (HpH II), have been characterized by Mössbauer, extended X-ray absorption fine structure (EXAFS) and UV-vis absorption spectroscopies. The proportions of the two forms are pH-dependent and the pH conversion between HpH II and LpH II is irreversible. Considering (1) the Mössbauer parameters evaluated for four related models by density functional theory methods, (2) the existence of two different Fe-O(ferryl) bond lengths (1.80 and 1.66 A) compatible with our EXAFS data and (3) the pH dependence of the alpha band to beta band intensity ratio in the absorption spectra, we attribute the LpH II compound to a protonated ferryl Fe(IV)-OH complex (Fe-O approximately 1.80 A), whereas the HpH II compound corresponds to the classic ferryl Fe(IV)=O complex (Fe=O approximately 1.66 A). The large quadrupole splitting value of LpH II (measured 2.29 mm s(-1) vs. computed 2.15 mm s(-1)) compared with that of HpH II (measured 1.47 mm s(-1) vs. computed 1.46 mm s(-1)) reflects the protonation of the ferryl group. The relevancy and involvement of such (Fe(IV)=O/Fe(IV)-OH) species in the reactivity of catalase, peroxidase and chloroperoxidase are discussed.

International audience; The green complex S = 1 [(TPEN)FeO]2+ [TPEN = N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine] has been obtained by treating the [(TPEN)Fe]2+ precursor with meta-chloroperoxybenzoic acid (m-CPBA). This high-valent complex belongs to the emerging family of synthetic models of FeIV=O intermediates invoked during the catalytic cycle of biological systems. This complex exhibits spectroscopic characteristics that are similar to those of other models reported recently with a similar amine/pyridine environment. Thanks to its relative stability, vibrational data in solution have been obtained by Fourier transform infrared. A comparison of the Fe=O and Fe=18O wavenumbers reveals that the Fe-oxo vibration is not a pure one. The ability of the green complex to oxidize small organic molecules has been studied. Mixtures of oxygenated products derived from two- or four-electron oxidations are obtained. The reactivity of this [FeO]2+ complex is then not straightforward, and different mechanisms may be involved.

Reaction of the unsymmetrical phenol ligand 2-((bis(2-pyridylmethyl)amino)methyl)-6-(((2-pyridylmethyl)benzylamino)methyl)-4-methylphenol (HL-Bn) or its 2,6-dichlorobenzyl analogue (HL-BnCl(2)) with Fe(H(2)O)(6)(ClO(4))(2) in the presence of disodium m-phenylenedipropionate (Na(2)(mpdp)) followed by exposure to atmosphere affords the diiron(II,III) complexes [Fe(2)(L-Bn)(mpdp)(H(2)O)](ClO(4))(2) and [Fe(2)(L-BnCl(2))(mpdp)(CH(3)OH)](ClO(4))(2), respectively. The latter complex has been characterized by X-ray crystallography. It crystallizes in the monoclinic system, space group P2(1)/n, with a = 13.3095(14) A, b = 20.1073(19) A, c = 19.4997(19) A, alpha = 90 degrees, beta = 94.471(2) degrees, gamma = 90 degrees, V = 5202.6(9) A(3), and Z = 4. The structure of the compound is very similar to that of [Fe(2)(L-Bn)(mpdp)(H(2)O)](BPh(4))(2) determined earlier, except for the replacement of a water by a methanol on the ferrous site. Magnetic measurements of [Fe(2)(L-Bn)(mpdp)(H(2)O)](BPh(4))(2) reveal that the two high-spin Fe ions are moderately antiferromagnetically coupled (J = -3.2(2) cm(-)(1)). Upon dissolution in acetonitrile the terminal ligand on the ferrous site is replaced by a solvent molecule. The acetonitrile-water exchange has been investigated by various spectroscopic techniques (UV-visible, NMR, Mössbauer) and electrochemistry. The substitution of acetonitrile by water is clearly evidenced by Mössbauer spectroscopy by a reduction of the quadrupole splitting value from 3.14 to 2.41 mm/s. In addition, it causes a 210 mV downshift of the oxidation potential of the ferrous site and a similar reduction of the stability domain of the mixed-valence state. Exhaustive electrolysis of a solution of [Fe(2)(L-Bn)(mpdp)(H(2)O)](2+) shows that the aqua diferric species is not stable and undergoes a chemical reaction which can be partly reversed by reduction to the mixed-valent state. This and other electrochemical observations suggest that upon oxidation of the diiron center to the diferric state the aqua ligand is deprotonated to a hydroxo. This hypothesis is supported by Mössbauer spectroscopy. Indeed, this species possesses a large quadrupole splitting value (DeltaE(Q)or= 1.0 mm.s(-)(1)) similar to that of analogous complexes with a terminal phenolate ligand. This study illustrates the drastic effects of aqua ligand exchange and deprotonation on the electronic structure and redox potentials of diiron centers.

Superoxide reductase (SOR) is an Fe protein that catalyzes the reduction of superoxide to give H(2)O(2). Recently, the mutation of the Glu47 residue into alanine (E47A) in the active site of SOR from Desulfoarculus baarsii has allowed the stabilization of an iron-peroxo species when quickly reacted with H(2)O(2) [Math{\'e} et al. (2002) J. Am. Chem. Soc. 124, 4966-4967]. To further investigate this non-heme peroxo-iron species, we have carried out a M{\"o}ssbauer study of the (57)Fe-enriched E47A SOR from D. baarsii reacted quickly with H(2)O(2). Considering the M{\"o}ssbauer data, we conclude, in conjunction with the other spectroscopic data available and with the results of density functional calculations on related models, that this species corresponds to a high-spin side-on peroxo-Fe(3+) complex. This is one of the first examples of such a species in a biological system for which M{\"o}ssbauer parameters are now available: delta(/Fe) = 0.54 (1) mm/s, DeltaE(Q) = -0.80 (5) mm/s, and the asymmetry parameter eta = 0.60 (5) mm/s. The M{\"o}ssbauer and spin Hamiltonian parameters have been evaluated on a model from the side-on peroxo complex (model 2) issued from the oxidized iron center in SOR from Pyrococcus furiosus, for which structural data are available in the literature [Yeh et al. (2000) Biochemistry 39, 2499-2508]. For comparison, similar calculations have been carried out on a model derived from 2 (model 3), where the [CH(3)-S](1)(-) group has been replaced by the neutral [NH(3)](0) group [Neese and Solomon (1998) J. Am. Chem. Soc. 120, 12829-12848]. Both models 2 and 3 contain a formally high-spin Fe(3+) ion (i.e., with empty minority spin orbitals). We found, however, a significant fraction (approximately 0.6 for 2, approximately 0.8 for 3) of spin (equivalently charge) spread over two occupied (minority spin) orbitals. The quadrupole splitting value for 2 is found to be negative and matches quite well the experimental value. The computed quadrupole tensors are rhombic in the case of 2 and axial in the case of 3. This difference originates directly from the presence of the thiolate ligand in 2. A correlation between experimental isomer shifts for Fe(3+) mononuclear complexes with computed electron densities at the iron nucleus has been built and used to evaluate the isomer shift values for 2 and 3 (0.56 and 0.63 mm/s, respectively). A significant increase of isomer shift value is found upon going from a methylthiolate to a nitrogen ligand for the Fe(3+) ion, consistent with covalency effects due to the presence of the axial thiolate ligand. Considering that the isomer shift value for 3 is likely to be in the 0.61-0.65 mm/s range [Horner et al. (2002) Eur. J. Inorg. Chem., 3278-3283], the isomer shift value for a high-spin eta(2)-O(2) Fe(3+) complex with an axial thiolate group can be estimated to be in the 0.54-0.58 mm/s range. The occurrence of a side-on peroxo intermediate in SOR is discussed in relation to the recent data published for a side-on peroxo-Fe(3+) species in another biological system [Karlsson et al. (2003) Science 299, 1039-1042]., Comment: Biochemistry, American Chemical Society, 2004, pp.8815-25

International audience; Ferric uptake regulation protein (Fur) is a global regulator, ubiquitous in Gram negative bacteria, that acts as a transcriptional repressor when it binds ferrous ion. Fur is involved in responses to several types of stress related to iron metabolism, such as stress induced by nitric oxide (NO) generated by macrophages against bacterial invasion. NO was recently shown to react with Fe(2+) ions in FeFur (iron substituted Fur protein) leading to an Fur bound iron-nitrosyl complex, unable to bind DNA, and characterized by a g = 2.03 EPR signal, associated with an S = (1)/(2) ground state. This electronic configuration could arise from either a mononitrosyl-iron [Fe(NO)](7) or a dinitrosyl-iron [Fe(NO)(2)](9) complex. The use of several spectroscopic tools such as EPR, ENDOR, FTIR, Mössbauer, and UV-visible spectroscopies as well as mass spectrometry analysis was necessary to characterize the iron-nitrosyl species in Fur. Furthermore, changes of C132 and C137 into glycines by site directed mutagenesis reveal that neither of the two cysteines is required for the formation of the g = 2.03 signal. Altogether, we found that two species are responsible for Fur inhibition in NO stress conditions: the major species, S(1/2), is an [Fe(NO)(2)](9) (S = (1)/(2)) complex without bound thiolate and the minor species is probably a diamagnetic [Fe(NO)(2)](8) (S = 0) complex. This is the first characterization of these physiologically relevant species potentially linking iron metabolism and the response to NO toxicity in bacteria.

International audience; Reaction of the unsymmetrical phenol ligand 2-((bis(2-pyridylmethyl)amino)methyl)-6-(((2-pyridylmethyl)benzylamino)methyl)-4-methylphenol (HL-Bn) or its 2,6-dichlorobenzyl analogue (HL-BnCl2) with Fe(H2O)6(ClO4)2 in the presence of disodium m-phenylenedipropionate (Na2(mpdp)) followed by exposure to atmosphere affords the diiron(II,III) complexes [Fe2(L-Bn)(mpdp)(H2O)](ClO4)2 and [Fe2(L-BnCl2)(mpdp)(CH3OH)](ClO4)2, respectively. The latter complex has been characterized by X-ray crystallography. It crystallizes in the monoclinic system, space group P21/n, with a = 13.3095(14) Å, b = 20.1073(19) Å, c = 19.4997(19) Å, = 90, = 94.471(2), = 90, V = 5202.6(9) Å3, and Z = 4. The structure of the compound is very similar to that of [Fe2(L-Bn)(mpdp)(H2O)](BPh4)2 determined earlier, except for the replacement of a water by a methanol on the ferrous site. Magnetic measurements of [Fe2(L-Bn)(mpdp)(H2O)](BPh4)2 reveal that the two high-spin Fe ions are moderately antiferromagnetically coupled (J = -3.2(2) cm-1). Upon dissolution in acetonitrile the terminal ligand on the ferrous site is replaced by a solvent molecule. The acetonitrile-water exchange has been investigated by various spectroscopic techniques (UV-visible, NMR, Mössbauer) and electrochemistry. The substitution of acetonitrile by water is clearly evidenced by Mössbauer spectroscopy by a reduction of the quadrupole splitting value from 3.14 to 2.41 mm/s. In addition, it causes a 210 mV downshift of the oxidation potential of the ferrous site and a similar reduction of the stability domain of the mixed-valence state. Exhaustive electrolysis of a solution of [Fe2(L-Bn)(mpdp)(H2O)]2+ shows that the aqua diferric species is not stable and undergoes a chemical reaction which can be partly reversed by reduction to the mixed-valent state. This and other electrochemical observations suggest that upon oxidation of the diiron center to the diferric state the aqua ligand is deprotonated to a hydroxo. This hypothesis is supported by Mössbauer spectroscopy. Indeed, this species possesses a large quadrupole splitting value (EQ 1.0 mm·s-1) similar to that of analogous complexes with a terminal phenolate ligand. This study illustrates the drastic effects of aqua ligand exchange and deprotonation on the electronic structure and redox potentials of diiron centers.

The tetrapodal pentaamine 2,6-C5H3N[CMe(CH2NH2)2]2 (pyN4, 1) forms a series of octahedral iron(II) complexes of general formula [Fe(L)(1)]Xn with a variety of small-molecule ligands L at the sixth coordination site (L = X = Br, n = 1 (2); L = CO, X = Br, n = 2 (3); L = NO, X = Br, n = 2 (4); L = NO+, X = Br, n = 3 (5); L = NO2-, X = Br, n = 1 (6)). The bromo complex, which is remarkably stable towards hydrolysis and oxidation, serves as the precursor for all other complexes, which may be obtained by ligand exchange, employing CO, NO, NOBF4, and NaNO2, respectively. All complexes have been fully characterised, including solid-state structures in most cases. Attempts to obtain single crystals of 6 produced the dinuclear complex [Fe2[mu 2-(eta 1-N: eta 1-O)-NO2](1)2]Br2PF6 (7), whose bridging NO2- unit, which is unsupported by bracketing ligands, is without precedent in the coordination chemistry of iron. Compound 2 has a high-spin electronic configuration with four unpaired electrons (S = 2), while the carbonyl complex 3 is low-spin (S = 0), as are complexes 5, 6 and 7 (S = 0 in all cases); the 19 valence electron nitrosyl complex 4 has S = 1/2. Complex 4 and its oxidation product, 5 ([Fe(NO)]7 and [Fe(NO)]6 in the Feltham-Enemark notation) may be interconverted by a one-electron redox process. Both complexes are also accessible from the mononuclear nitro complex 6: Treatment with acid produces the 18 valence electron NO+ complex 5, whereas hydrolysis in the absence of added protons (in methanolic solution) gives the 19 valence electron NO. complex 4, with formal reduction of the NO2- ligand. This reactivity mimicks the function of certain heme-dependent nitrite reductases. Density functional calculations for complexes 3, 4 and 5 provide a description of the electronic structures and are compatible with the formulation of iron(II) in all cases; this is derived from the careful analysis of the combined IR, ESR and Mossbauer spectroscopic data, as well as structural parameters.

The complexes [L(5)Fe(II)Cl]BPh(4) and [L(5)Fe(II)(H(2)O)](BPh(4))(2) (L(5) = N,N,N'-tris(2-pyridylmethyl)-N'-methyl-ethane-1,2-diamine) have been isolated. Bernal et al. (Bernal, J.; et al. J. Chem. Soc., Dalton Trans. 1995, 3667-3675) have prepared this ligand and the corresponding complex [L(5)Fe(II)Cl]PF(6). We obtained the structural data of [L(5)Fe(II)Cl]BPh(4) by X-ray diffraction. It crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 17.645(7) Å, b = 16.077(6) Å, c = 13.934(5) Å, V = 3953(3) Å(3), and Z = 4. It presents Fe(II)-N bond lengths close to 2.2 Å, typical of high-spin Fe(II). In solution the [L(5)Fe(II)(H(2)O)](BPh(4))(2) complex showed a dependence of spin state upon the nature of the solvent. It was high spin in acetone and changed to low spin in acetonitrile. This was detected by UV-vis spectroscopy and by (1)H NMR. Bernal et al. (ibidem) showed that these complexes in the presence of an excess of H(2)O(2) give a purple species, very likely the [L(5)Fe(III)(OOH)](2+) derivative, with spectroscopic signatures analogous to those of "activated bleomycin". The formation of [L(5)Fe(III)(OOH)](2+) is confirmed here by electrospray ionization mass spectrometry. We found that a L(5)/Fe system gave single-strand breaks on plasmid DNA in the presence of either a reducing agent (ascorbate) and air or oxidants (H(2)O(2), KHSO(5), MMPP) at 0.1mgr;M concentration. The methyl group in L(5) was substituted by a (CH(2))(5)N(CH(3))(3)(+) group in order to get higher affinity with DNA. The corresponding ligand L(5)(+) was used to prepare the complexes [L(5)(+)Fe(II)Cl]Y(2) (Y = BPh(4)(-), PF(6)(-), ClO(4)(-)) and [L(5)(+)Fe(II)Br](PF(6))(2). The crystal structure of [L(5)(+)Fe(II)Cl](ClO(4))(2) was solved. It crystallizes in the monoclinic space group P2(1)/a with a = 14.691(2) Å, b = 13.545(2) Å, c = 17.430(2) Å, beta = 93.43(1) degrees, V = 3462(1) Å(3), and Z = 4. The Fe(II)-ligand distances are similar to those of [L(5)Fe(II)Cl]BPh(4). At the relatively low concentration of 0.01mgr;M, [L(5)(+)Fe(II)Br](2+) promoted DNA breaks. The reaction was not inhibited by hydroxyl radical scavengers. The reaction might involve a nondiffusible oxygen reactive species, either a coordinated hydroperoxide or a high-valent metal-oxo entity.

The compound [Mn(III)(2)OL(2)](ClO(4))(2).2.23CHCl(3).0.65CH(2)Cl(2) where L(-) is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicyliden-1,2-diaminoethane ligand, has been synthesized. The complex dication [Mn(III)(2)OL(2)](2+) contains a linear Mn(III)-O-Mn(III) unit with a Mn-Mn distance of 3.516 Å. The pentadentate ligand L(-) wraps around the Mn(III) ion. Electrochemically, it is possible to prepare the one electron oxidized trication [Mn(2)OL(2)](3+) which crystallizes as [Mn(2)OL(2)](ClO(4))(2.37)(PF(6))(0.63).1.5CH(3)CN. The complex trication [Mn(2)OL(2)](3+) contains a Mn(III)-O-Mn(IV) unit with a Mn-Mn distance of 3.524 Å and a Mn-O-Mn angle of 178.7(2) degrees. The contraction of the coordination sphere around the Mn(IV) is clearly observed. The [Mn(2)OL(2)](2+) dication possesses a S = 0 electronic ground state with J = -216 cm(-)(1) (H = -JS(1)().S(2)()), whereas the [Mn(2)OL(2)](3+) trication shows a S = (1)/(2) ground state with J = -353 cm(-)(1). The UV-visible spectrum of [Mn(2)OL(2)](3+) exhibits an intense absorption band (epsilon = 3040 M(-)(1) cm(-)(1)) centered at 570 nm assigned to a phenolate --Mn(IV) charge-transfer transition. The potentials of the redox couples determined by cyclic voltammetry are E degrees ([Mn(2)OL(2)](3+)/[Mn(2)OL(2)](2+)) = 0.54 V/saturated calomel electrode (SCE) and E degrees ([Mn(2)OL(2)](4+)/[Mn(2)OL(2)](3+)) = 0.99 V/SCE. Upon oxidation at 1.3 V/SCE, the band at 570 nm shifts to 710 nm (epsilon = 2500 M(-)(1) cm(-)(1)) and a well-defined band appears at 400 nm which suggests the formation of a phenoxyl radical. The [Mn(2)OL(2)](3+)( )()complex exhibits a 18-line X-band electron paramagnetic resonance (EPR) spectrum which has been simulated with rhombic tensors |A(1)(x)()| = 160 x 10(-)(4) cm(-)(1); |A(1)(y)()| = 130 x 10(-)(4) cm(-)(1); |A(1)(z)()| = 91 x 10(-)(4) cm(-)(1); |A(2)(x)()| = 62 x 10(-)(4) cm(-)(1); |A(2)(y)()| = 59 x 10(-)(4) cm(-)(1); |A(2)(z)()| = 62 x 10(-)(4) cm(-)(1) and g(x)() = 2.006; g(y)() = 1.997; g(z)() = 1.982. This EPR spectrum( )()shows that the 16-line paradigm related to a large antiferromagnetic exchange coupling and a low anisotropy can be overcome by a large rhombic anisotropy. Molecular orbital calculations relate this rhombicity to the nature of the orbital describing the extra electron on Mn(III). This orbital has a majority but not pure d(z)()2 contribution (with the z axis perpendicular to the Mn-Mn axis). Low-temperature resonance Raman spectroscopy on an acetonitrile solution of [Mn(2)OL(2)](4+) prepared at -35 degrees C indicated the formation of a phenoxyl radical. This suggests that the ligand was oxidized rather than the Mn(III)Mn(IV) pair to Mn(IV)Mn(IV), which illustrates the difficulty to store a second positive charge in a short range of potential in a manganese mono-mgr;-oxo pair. The relevance of these results to the study of the photosynthetic oxygen evolving complex is discussed.

The Mn4 complex which is involved in water oxidation in photosystem II (PSII) is known to exhibit two types of EPR signals in the S2 state, one of the five redox states of the enzyme cycle: either a multiline signal (S = 1/2) or a signal at g = 4.1 (S = 3/2 or S= 5/2). The S = 1/2 state can be converted to that responsible for the g = 4.1 signal upon the absorption of near-infrared (IR) light [Boussac, A., Girerd, J.-J., and Rutherford, A.W. (1996) Biochemistry 35, 6984-6989]. It is shown here that a third state gives rise to signals at g = 10 and 6. This state is formed by IR illumination of the S = 1/2 state at 65 K, a temperature where IR illumination leads to the loss of the S = 1/2 signal but to no formation of the g = 4.1 state. On the basis of the corresponding decrease of the S = 1/2 state, the new state can be trapped in approximately 40% of the PSII centers. Warming of the sample above 65 K, in the dark, leads to the loss of the g = 10 and 6 resonances with the corresponding appearance of the g = 4.1 signal. It is suggested that the IR-induced conversion of the S = 1/2 state into the g = 4.1 state at 150 K involves the transient formation of the new state. The new state is attributed to a S = 5/2 state of the Mn4 complex (although a S value5/2 is also a possibility). Spectral simulations indicate an E/D ratio of -0.05 with D/= 1 cm-1. The resonances at g = 10 and 6 correspond to the gz of the +/-5/2 and +/-3/2 transition, respectively. The temperature-dependent conversion of this S = 5/2 state into the g = 4.1 state is proposed to be due to relaxation of the ligand environment around the Mn4 cluster that leads to a change in the zero field splitting parameters, assuming an S = 5/2 value for the g = 4.1 state. The new form of the S2 state reported here may explain some earlier data where the S2 state was present and yet not detectable as either a S = 1/2 or a g = 4.1 EPR signal.

International audience; The active site of superoxide reductase SOR consists of an Fe2+ center in an unusual [His4 Cys1] square-pyramidal geometry. It specifically reduces superoxide to produce H2O2. Here, we have reacted the SOR from Desulfoarculus baarsii directly with H2O2. We have found that its active site can transiently stabilize an Fe3+-peroxo species that we have spectroscopically characterized by resonance Raman. The mutation of the strictly conserved Glu47 into alanine results in a stabilization of this Fe3+-peroxo species, when compared to the wild-type form. These data support the hypothesis that the reaction of SOR proceeds through such a Fe3+-peroxo intermediate. This also suggests that Glu47 might serve to help H2O2 release during the reaction with superoxide.

Scaling phenomenon, mainly related to the precipitation of calcium carbonate(CaCO3), is widely encountered in industry using water. It is necessary to find solutions inorder to control scale deposition.This thesis describes the influence of two metallic cations, copper (II) and zinc (II),on the CaCO3 precipitation. The first part focuses on the inhibitory effect of these ions onscaling in synthetic waters of 25 and 50 °F. Investigations are conducted using FastControlled Precipitation method (FCP) and Scaling Quartz Crystal Microbalance (SQCM).These measurements make it possible to follow the nucleation and growth processes ofcalcium carbonate in solution and on the pre-calcareous metallic surface. The results showthat Zn2+ and Cu2+ ions play an important role in the kinetics of CaCO3 formation. They actas retarders of the scaling phenomenon.The second part is devoted to the study of the scaling phenomenon on a steel surfacepretreated with an organic-inorganic hybrid film (polysiloxane-based films) already testedagainst corrosion, developed in an original way using the sol–gel process. The QCM andchronoamperometric (CA) methods allowed the monitoring of calcium carbonateprecipitation kinetics on the surface covered by the synthesized polymers doped with copperand zinc cations. The idea is to act directly on the metallic surface in contact with the waterwithout modifying the composition and the nature of the water in question. The obtainedresults show that the doping of the metal cations improves the anti-scaling effect of the film.; Le phénomène d’entartrage, principalement lié à la précipitation du carbonate decalcium (CaCO3) est très largement rencontré dans les industries et les circuits utilisant del’eau. Sa présence entraîne des problèmes à la fois techniques et économiques. La préventionet la mise en place de moyens de lutte contre l’entartrage constituent une préoccupationmajeure des chercheurs qui s’intéressent à ce phénomène.Ce travail de thèse décrit l’influence des cations métalliques cuivre (II) et zinc (II)sur la précipitation de CaCO3. La première partie met l’accent sur l’effet inhibiteur de cesions vis-à-vis de l’entartrage, dans des eaux synthétiques de 25 et 50°F. Les investigationssont menées en utilisant la méthode de précipitation contrôlée rapide (PCR) et lamicrobalance à cristal de quartz avec une surface pré-entartrée (SQCM). Ces mesurespermettent de suivre le processus de germination et de croissance du carbonate de calciumen solution et sur la surface métallique pré-entartrée. Les résultats montrent que les ions Zn2+et Cu2+ jouent un rôle important sur la cinétique de la formation de CaCO3. Ils agissentcomme des retardateurs du phénomène d’entartrage.La deuxième partie est dédiée à l’étude du phénomène d’entartrage sur une surfaceen acier prétraitée par un film hybride organique-inorganique (films à bases depolysiloxanes) déjà testé contre la corrosion, élaboré par le procédé sol–gel. Les méthodesQCM et la chronoampérométrie (CA) ont permis le suivi de la cinétique de précipitation ducarbonate de calcium sur la surface recouverte par les polymères synthétisés dopés auxcations cuivre et zinc. L’idée est d’agir directement sur la surface métallique en contact del’eau sans modifier la composition et la nature de l’eau en question. Les résultats obtenusont montré que le dopage des cations métalliques améliore l’effet antitartre du film.