Gilles Montavon

Investigation of alendronate-doped Apatitic Cements as a Potential Technology for the Prevention of Osteoporotic Hip Fractures: Critical Influence of the Drug Introduction Mode on the In Vitro Cement Properties.

Combination of a bisphosphonate (BP) anti-osteoporotic drug, alendronate, with an apatitic calcium phosphate cement does not significantly affect the main properties of the biomaterial, in terms of injectability and setting time, provided that the BP is introduced chemisorbed onto calcium-deficient apatite, one of the components of the cement. In contrast to other modes of introducing the BP into the cement formulation, this mode allows to minimize alendronate release in the cement paste, thus limiting the setting retardant effect of the BP. An original approach based on high frequency impedance measurements is found to be a convenient method for in situ monitoring of the cement setting reaction. The release profile of the drug from a cement block under continuous flow conditions can be well described using a coupled chemistry/transport model, under simulated in vivo conditions. The results show that the released alendronate concentration is expected to be much lower than the cytotoxic concentration.

Astatine Standard Redox Potentials and Speciation in Acidic Medium

A combined experimental and theoretical approach is used to define astatine (At) speciation in acidic aqueous solution and to answer the two main questions raised from literature data: does At(0) exist in aqueous solution and what is the chemical form of At(+III), if it exists. The experimental approach considers that a given species is characterized by its distribution coefficient (D) experimentally determined in a biphasic system. The change in speciation arising from a change in experimental conditions is observed by a change in D value. The theoretical approach involves quasi-relativistic quantum chemistry calculations. The results show that At at the oxidation state 0 cannot exist in aqueous solution. The three oxidation states present in the range of water stability are At(-I), At(+I), and At(+III) and exist as At(-), At(+), and AtO(+), respectively, in the 1-2 pH range. The standard redox potentials of the At(+)/At(-) and AtO(+)/At(+) couples have been determined, the respective values being 0.36 +/- 0.01 and 0.74 +/- 0.01 V vs NHE.

Review of chemical and radiotoxicological properties of polonium for internal contamination purposes

The discovery of polonium (Po) was first published in July, 1898 by P. Curie and M. Curie. It was the first element to be discovered by the radiochemical method. Polonium can be considered as a famous but neglected element: only a few studies of polonium chemistry have been published, mostly between 1950 and 1990. The recent (2006) event in which (210)Po evidently was used as a poison to kill A. Litvinenko has raised new interest in polonium. 2011 being the 100th anniversary of the Marie Curie Nobel Prize in Chemistry, the aim of this review is to look at the several aspects of polonium linked to its chemical properties and its radiotoxicity, including (i) its radiochemistry and interaction with matter; (ii) its main sources and uses; (iii) its physicochemical properties; (iv) its main analytical methods; (v) its background exposure risk in water, food, and other environmental media; (vi) its biokinetics and distribution following inhalation, ingestion, and wound contamination; (vii) its dosimetry; and (viii) treatments available (decorporation) in case of internal contamination.

Investigation of astatine(III) hydrolyzed species: experiments and relativistic calculations.

This work aims to resolve some controversies about astatine(III) hydroxide species present in oxidant aqueous solution. AtO(+) is the dominant species existing under oxidizing and acidic pH conditions. This is consistent with high-performance ion-exchange chromatography data showing the existence of one species holding one positive charge. A change in speciation occurs as the pH changes from 1 to 4, while remaining under oxidizing conditions. Dynamic experiments with ion-exchange resins evidence the existence of a neutral species witnessed by its elution in the void volume. Batch-experiments using a competition method show the exchange of one proton indicating the formation of the AtO(OH) species. The hydrolysis thermodynamic constant, extrapolated to zero ionic strength, was determined to be 10(-1.9). This value is supported by two-component relativistic quantum calculations and therefore allows disclosing unambiguously the structure of the formed species.

Sorption of Cs, Ni, Pb, Eu(III), Am(III), Cm, Ac(III), Tc(IV), Th, Zr, and U(IV) on MX 80 bentonite: An experimental approach to assess model uncertainty

A multi-site surface complexation/ion exchange model for dispersed MX 80 bentonite has been calibrated, considering the dissolution properties of the constituting mineral assemblage, for sorption of a large number of radionuclides, using experimental data from the present study together with well constrained literature data. Emphasis was on tri- and tetravalents actinides and fission products and reducing groundwater compositions.

Extraction of astatine-211 in diisopropylether (DIPE)

Abstract The extraction mechanism of astatine-211 in diisopropylether (DIPE) is studied by analyzing the effect of the nature of the aqueous solution and organic solvent on the distribution coefficients characterizing the ratio of organic and aqueous concentration of astatine (D). On the one hand, at a given pH value, D was shown to be independant of the nature and concentration of the counter-ion present in the aqueous solution (Cl-, ClO4-, NO3-). On the other hand, the nature of the organic solvent had a strong effect. D increases as the polarity of the organic solvent increases. These experimental observations are explained by the solvation of astatine by the organic solvent. The back-extraction of astatine from the organic to the aqueous phase is efficient in basic conditions. This is explained by the formation of a hydrolyzed species of astatine presenting no affinity for DIPE. Hydrolysis constants of astatine are deduced from experimental data (logβ1=-3.0±0.1 and logβ2=-14.2±0.1).

Selenide retention onto pyrite under reducing conditions

Summary Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it turns out to be a sorption sink for certain radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize selenide (Se(-II)). Due to the fact that pyrite surface oxidizes readily, potentials were applied in order to minimise its surface evolution, and ensure the reducing conditions necessary for stabilizing Se(-II). The sorption experiments were carried out in NaCl electrolyte and were amperometrically controlled. After only several minutes of reaction, at least 97% of Se(-II) initially present in solution was disappeared. The Kd values vary from 7–65 L/g and the isotherm curve shows site saturation at higher initial selenide concentrations and no pH-dependence. By means of several spectroscopic techniques, the reaction mechanism was investigated. The XRD and in situ XANES results indicate the presence of Se(0) on pyrite surface, which explain the rapid disappearance of Se observed in the sorption experiments. Moreover, XPS results obtained from Se-reacted pyrite particles reveal cleavage of S–S bonding which resulted in formation of S2− on pyrite surface. Thus, we conclude that Se(-II) can be immobilized by pyrite via surface redox reaction: ≡FeS2 + HSe− ⇔ ≡FeS + Se(0) + HS−.

Design and properties of novel gallium-doped injectable apatitic cements

UNLABELLED Different possible options were investigated to combine an apatitic calcium phosphate cement with gallium ions, known as bone resorption inhibitors. Gallium can be either chemisorbed onto calcium-deficient apatite or inserted in the structure of β-tricalcium phosphate, and addition of these gallium-doped components into the cement formulation did not significantly affect the main properties of the biomaterial, in terms of injectability and setting time. Under in vitro conditions, the amount of gallium released from the resulting cement pellets was found to be low, but increased in the presence of osteoclastic cells. When implanted in rabbit bone critical defects, a remodeling process of the gallium-doped implant started and an excellent bone interface was observed. STATEMENT OF SIGNIFICANCE The integration of drugs and materials is a growing force in the medical industry. The incorporation of pharmaceutical products not only promises to expand the therapeutic scope of biomaterials technology but to design a new generation of true combination products whose therapeutic value stem equally from both the structural attributes of the material and the intrinsic therapy of the drug. In this context, for the first time an injectable calcium phosphate cement containing gallium was designed with properties suitable for practical application as a local delivery system, implantable by minimally invasive surgery. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

Effective bond orders from two-step spin–orbit coupling approaches: The I{sub 2}, At{sub 2}, IO{sup +}, and AtO{sup +} case studies

The nature of chemical bonds in heavy main-group diatomics is discussed from the viewpoint of effective bond orders, which are computed from spin-orbit wave functions resulting from spin-orbit configuration interaction calculations. The reliability of the relativistic correlated wave functions obtained in such two-step spin-orbit coupling frameworks is assessed by benchmark studies of the spectroscopic constants with respect to either experimental data, or state-of-the-art fully relativistic correlated calculations. The I2, At2, IO(+), and AtO(+) species are considered, and differences and similarities between the astatine and iodine elements are highlighted. In particular, we demonstrate that spin-orbit coupling weakens the covalent character of the bond in At2 even more than electron correlation, making the consideration of spin-orbit coupling compulsory for discussing chemical bonding in heavy (6p) main group element systems.

Condensation mechanisms of tetravalent technetium in chloride media

Summary The condensation mechanisms of tetravalent technetium in chloride media were studied in the pH range 0–1.5. A new dimer complex of Tc(IV) has thus been discovered, Tc2OCl104−. Spectroscopic and kinetics studies showed that the formation of this compound resulted from the condensation of TcCl5(H2O)−. An EXAFS study indicates that the dimer displays a [Tc-O-Tc]6+ structure. As the pH increases, UV-visible measurements showed a cyclization of [Tc-O-Tc]6+ into [Tc(μO)2Tc]4+ leading, in fine, to the precipitation of TcO2·x H2O. The aquation constant (Kaq) of TcCl62− into TcCl5(H2O)− and the dimerisation constant (logKdim) of TcCl5(H2O)− into Tc2OCl104− were determined to be 2.20±0.26 and 4.68±0.09, respectively.