Design of a ligand suitable for sensitive uranyl analysis in aqueous solutions

<div><p>Several ligands were designed as plausible reagents for the spectrophotometric analysis of uranyl in aqueous solutions. The ligand  = 3,3′-(ethane-1,2-diylbis(methylazanediyl))bis(methylene)bis(4-hydroxybenzenesulfonate) was found to fit best the requirements. The results point out that carboxylate substituents compete with the phenolate substituents as binding sites to the central uranium cation and therefore decrease the usefulness of ligands containing both carboxylate and phenolate substituents as analytical spectrophotometric reagents.</p></div

5-[2,4-Dihydroxy-5-(5-hydroxy-2,4,6-trioxo-3,5-dihydro-1H-pyrimidin-5-yl)-3-methoxyphenyl]-5-hydroxy-3,5-dihydro-1H-pyrimidine-2,4,6-trione pentahydrate

The title compound, C15H12N4O11·5H2O, has a `propeller-like' structure. The two alloxan units have screw-boat conformations. Their mean planes are normal to the central aromatic ring with dihedral angles of 87.91 (7) and 88.27 (7)°, and they are inclined to one another by 40.86 (7)°. In the crystal, molecules are linked via O—H...O and N—H...O hydrogen bonds, forming a three-dimensional framework. There are also C—H...O hydrogen bonds present within the framework

Different oxidation mechanisms of Mn^II(polyphosphate)_n by the radicals and

<p>The kinetics and mechanisms of the oxidation of and of by the biological relevant radicals and were studied. The rate constants of the oxidations by both radicals are faster for the complexes than for the complexes, though the redox potentials predict the reverse order of reactivity. Surprisingly, the results point out that these two radicals react via different mechanisms. Thus, the increase in the concentration of the ligands decreases the rate constants of the oxidations by , whereas it increases the rate constants of the oxidation by . These results point out that these radicals behave differently though both are inner-sphere oxidants. The plausible mechanisms of reaction of these radicals are discussed.</p

Spectroscopic, electrochemical, and structural aspects of the Ce(IV)/Ce(III) DOTA redox couple chemistry in aqueous solutions

<p>The redox potential of the Ce(IV)/Ce(III) DOTA is determined to be 0.65 V <i>versus</i> SCE, pointing out a stabilization of ~13 orders of magnitude for the Ce(IV)DOTA complex, as compared to Ce(IV)_aq. The Ce(III)DOTA after electrochemical oxidation yields a Ce(IV)DOTA complex with a <i>t</i>_1/2 ~3 h and which is suggested to retain the “in cage” geometry. Chemical oxidation of Ce(III)DOTA by diperoxosulfate renders a similar Ce(IV)DOTA complex with the same <i>t</i>_1/2. From the electrochemical measurements, one calculates logK (Ce(IV)DOTA²⁻) ~ 35.9. Surprisingly, when Ce(IV)DOTA is obtained by mixing Ce(IV)_aq with DOTA, a different species is obtained with a 2 : 1(M : L) stoichiometry. This new complex, Ce(IV)DOTACe(IV), shows redox and spectroscopic features which are different from the electrochemically prepared Ce(IV)DOTA. When one uses thiosulfate as a reducing agent of Ce(IV)DOTACe(IV), one gets a prolonged lifetime of the latter. The reductant seems to serve primarily as a coordinating ligand with a geometry which does not facilitate inner sphere electron transfer. The reduction process rate in this case could be dictated by an outer sphere electron transfer or DOTA exchange by S₂O₃²⁻. Both Ce(IV)DOTA and Ce(IV)DOTACe(IV) have similar kinetic stability and presumably decompose via decarboxylation of the polyaminocarboxylate ligand.</p