Jean Rimbault

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.

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.

Coordination Mode and Kinetic Behavior of the Tetracarbonatozirconate Ion

by Anne Veylanda), Jean Rimbaulta)*, Laurent Duponta), Jean-Claude Pierrarda), Michel Aplincourta), SteÂphane Bourgb), Jean-Marc Nuzillardb), and Jean-Francois Angiboustc) a) GRECI, UFR des Sciences Exactes et Naturelles, Universite de Reims Champagne-Ardenne, BP 1039, F-51687 Reims Cedex 2 b) Laboratoire de Pharmacognosie UPRESA 6013, Universite de Reims Champagne-Ardenne, BP 1039, F-51687 Reims Cedex 2 c) Laboratoire de Spectroscopie BiomoleÂculaire, Universite de Reims Champagne-Ardenne, BP 1039, F-51687 Reims Cedex 2

Investigation of the tetracarbonatozirconate ion by electrospray mass spectrometry in aqueous media

Abstract Reported here is the study of zirconium (IV) aqueous solutions in carbonate media by electrospray ionisation mass spectrometry (ESI–MS). Spectra analysis lead to consider the existence in the spray of the initial pseudomolecular labile species [Zr(CO 3 ) 4 (HCO 3 )] 5− , x H + , (6− x ) K + (or Na + ). The existence of this species confirms the associative exchange mechanism of carbonate ions with [Zr(CO 3 ) 4 ] 4− ion.

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.

Synthesis and Physicochemical Characterization of 1,4,7,10-Tetra (2-glutaryl)-1,4,7,10 Tetraazacyclododecane Lanthanide Complexes

To describe a new tetra-(carboxyethyl) derivative of Gd-DOTA called P730 Gd (1): Figure 1. P730 Gd is a precursor in the synthesis of new macromolecular MRI contrast agents. The inner sphere contribution to the relaxivity of gadolinium complexes is determined by the rotational correlation time of the complex R, the water residence time M in the first coordination shell and the electronic relaxation time S (2). Each of these main relaxometric parameters is influenced by the structural characteristics of the complexes. Consequently, the structural and the physicochemical properties of each P730 diastereoisomer have been studied by crystallography, NMR and luminescence. In order to avoid complex dissociation, new Gd3 chelates should be characterized by high thermodynamic stability and transmetallation inertness, therefore the thermodynamic stability constant of P730 Gd was determined and its stability in a model of transmetallation was assessed. MATERIALS AND METHODS

Spectrophotometric studies of the reactions of tertiary bisdiphenylphosphines Ph2P(CH2)nPPh2 with n = 1, 2 and 3 on dibromobis(triphenylphosphine)cobalt(II), in benzene solution. Formation of penta-coordinated complexes

Abstract The reactions of CoBr 2 (PPh 3 ) 2 at 25°C in benzene with Ph 2 P(CH 2 ) n PPh 2 with n = 1 (dpm), n = 2 (dpe) and n = 3 (dpp) have been followed spectrophotometrically and by conductivity measurements in CH 2 Cl 2 . The addition and substitution steps of the bidentate bisphosphines LL on the initial cobalt complex have been identified and the equilibrium constants calculated at different wavelengths using least squares methods. With dpm, binuclear species are formed in three steps with bridging dpm molecules. With dpe and dpp, two steps are observed with the formation of the final red penta-coordinated complexes [CoBr(LL) 2 ]Br; the intermediate complexes are different in each case. The overall constant for the equilibrium CoBr 2 (PPh 3 ) 2 +2LLα[CoBr(LL) 2 ]Br+2PPh 3 is 1.06 x 10 5 for dpe and 1.20 x 10 3 for dpp, and depends on the size of the chelate rings.

Phosphine and phosphine oxide ligand substitution and redistribution on tetrahedral cobalt(II) complexes in benzene

Abstract The substitution equilibria in benzene (at 25°C): CoX2(PPh3)2+OPPh3⇄CoX2(OPPh3)(PPh3)+PPh3 and CoX2(OPPh3)(PPh3)+OPPh3⇄CoX2(OPPh3)2+PPh3 have been followed spectrophotometrically and equilibrium constants calculated. When X = Cl, K1 = 136 and K2 = 1.9; when X = Br, K1 = 22 and K2 = 1.6; when X = I, K1 = 37 and K2 = 1.4. The mixed complexes CoX2(OPPh3)(PPh3) have been isolated and their electronic spectra calculated. They are subject to redistribution equilibria in benzene: 2CoX2(OPPh3)(PPh3)⇄CoX2(OPPh3)2+CoX2(PPh3)2 with K = 0.014 for X = Cl; 0.071 for X = Br and 0.039 for X = I. The unusual order of the constants K1 and K is discussed in terms of electronic and steric effects.