Biomedical subjects

Thomas Vercouter

Publications and source records attributed to Thomas Vercouter.

4 recordsLinked to original sources

PubMed2006

Actinide speciation in relation to biological processes.

In case of accidental release of radionuclides into the environment, actinides represent a severe health risk to human beings following internal contamination (inhalation, ingestion or wound). For a better understanding of the actinide behaviour in man (in term of metabolism, retention, excretion) and in specific biological systems (organs, cells or biochemical pathways), it is of prime importance to have a good knowledge of the relevant actinide solution chemistry and biochemistry, in particular of the thermodynamic constants needed for computing actinide speciation. To a large extent, speciation governs bioavailability and toxicity of elements and has a significant impact on the mechanisms by which toxics accumulate in cell compartments and organs and by which elements are transferred and transported from cell to cell. From another viewpoint, speciation is the prerequisite for the design and success of potential decorporation therapies. The purpose of this review is to present the state of the art of actinide knowledge within biological media. It is also to discuss how actinide speciation can be determined or predicted and to highlight the areas where information is lacking with the aim to encourage new research efforts.

Actinoid Series Elements↗

PubMed2005

Sulfate complexation of trivalent lanthanides probed by nanoelectrospray mass spectrometry and time-resolved laser-induced luminescence.

Sulfate complexation of lanthanides is of great interest for predicting speciation of radionuclides in natural environments. The formation of LaSO4+(aq) in HNO3/H2SO4 aqueous solutions of low ionic strength (I) was studied by nanoelectrospray ionization mass spectrometry (nanoESI-MS). Several gaseous species containing LaSO4+ were detected. The formation constant of LaSO4+(aq) was determined and extrapolated to I = 0 (log = 3.5 +/- 0.3) by using a simple specific ion interaction theory (SIT) formula. This value supports the potential of nanoESI-MS for the study of kinetically labile species. The species La(SO4)(2-) was also detected. In addition, time-resolved laser-induced luminescence (TRLIL) was used to study Eu(III) speciation under ionic conditions of 0.02-0.05 M H+ (H2SO4/HClO4) and 0.4-2.0 M Na+ (Na2SO4/NaClO4). The data were interpreted with the species EuSO4+ (log = 3.7(8) +/- 0.1) and Eu(SO4)(2-) (log = 1.5 +/- 0.2). For extrapolating to I = 0, all of the major ions were taken into account through several SIT ion-pair parameters, epsilon. Most of the epsilon values were estimated by analogy to known parameters for similar ion-pair interactions using linear correlations, while epsilon(Eu)3+,SO4(2-) = 0.8(6) +/- 0.5 was fitted to the experimental data because, to date, SIT coefficients between multicharged species are not reported. The formation constants obtained here confirm some of those previously measured for Ln(III) and An(III) by various experimental techniques, and conversely do not give credit to the idea that in equilibrium conditions TRLIL and other spectroscopic techniques would provide stability constants of only inner-sphere complexes. The fluorescence lifetimes measured for EuSO4+ and Eu(SO4)(2-) were consistent with the replacement of one H2O molecule in the first coordination sphere of Eu3+ for each added SO4(2-) ligand, suggesting a monodentate SO4(2-) coordination.

Lanthanoid Series Elements↗

PubMed2005

Stabilities of the aqueous complexes Cm(CO3)33- and Am(CO3)33- in the temperature range 10-70 degrees C.

The carbonate complexation of curium(III) in aqueous solutions with high ionic strength was investigated below solubility limits in the 10-70 degrees C temperature range using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The equilibrium constant, K(3), for the Cm(CO(3))(2-) + CO(3)(2-) right harpoon over left harpoon Cm(CO(3))(3)(3-) reaction was determined (log K(3) = 2.01 +/- 0.05 at 25 degrees C, I = 3 M (NaClO(4))) and compared to scattered previously published values. The log K(3) value for Cm(III) was found to increase linearly with 1/T, reflecting a negligible temperature influence on the corresponding molar enthalpy change, Delta(r)H(3) = 12.2 +/- 4.4 kJ mol(-1), and molar entropy change, Delta(r)S(3) = 79 +/- 16 J mol(-1) K(-1). These values were extrapolated to I = 0 with the SIT formula (Delta(r)H(3) degrees = 9.4 +/- 4.8 kJ mol(-1), Delta(r)S(3) degrees = 48 +/- 23 J mol(-1) K(-1), log K(3) degrees = 0.88 +/- 0.05 at 25 degrees C). Virtually the same values were obtained from the solubility data for the analogous Am(III) complexes, which were reinterpreted considering the transformation of the solubility-controlling solid. The reaction studied was found to be driven by the entropy. This was interpreted as a result of hydration changes. As expected, excess energy changes of the reaction showed that the ionic strength had a greater influence on Delta(r)S(3) than it did on Delta(r)H(3).

Journal Article↗

PubMed2003

Fluorinated calixpyrroles: anion-binding extractants that reduce the Hofmeister bias.

Beta-octafluoro-meso-octamethylcalix[4]pyrrole (1) and beta-decafluoro-meso-decamethylcalix[5]pyrrole (2) were found to extract caesium salts of smaller anions (bromide and chloride for 1 and nitrate for 2) as effectively as that of iodide into nitrobenzene (NB) thereby overcoming the Hofmeister bias normally observed for processes of this type.

Journal Article↗