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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.

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; 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.

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.

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; 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.