No abstract

The complexation of lanthanum(III), europium(III), dysprosium(III), erbium(III), and lutetium(III) with D‐gluconic acid (LH) was studied by pH potentiometry and NMR. The set of complexes formed in aqueous solutions and their stability constants β were determined, and the results were compared to those previously found for praseodymium(III) (S. Giroux et al., Polyhedron 2000, 19, 1567). A regular evolution of the β values was observed along the lanthanide series, particularly for the neutral complex MLH−2 (where two hydroxy functions were deprotonated) with a selectivity similar to that of EDTA. For the ML2+ complex, where the ligand was coordinated via the carboxylate groups, the analysis of the 13C NMR pseudo‐contact shift showed that the carboxylate group was not bidentate and that there was a participation of the α‐hydroxy group in the coordination. The study of the complexation of PrIII with other hydroxy carboxylic acids: glyceric, threonic, 2‐hydroxybutanoic, and 3‐hydroxybutanoic acids confirms that in the complex MLH−2 the deprotonated hydroxy groups, that intervene in the coordination with the metal ion, are those in α and γ positions relative to the carboxylate group. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The solubilization of octylamidotartaric acid (C8T) and octanoic acid (C8C) in Triton X-100 and Brij 58 nonionic micelles has been studied by pHmetric and 1H NMR self-diffusion experiments. As both C8C and C8T exhibit acid-base properties, a distinction between the partition of the neutral acidic form, in terms of the partition coefficient KPH, and the partition of the charged basic form, in terms of the partition coefficient KP-, has been made. The acidity constants, Ka, of C8T and C8C in the presence of micelles have been evaluated from pHmetric experiments. For both solutes, an increase in the pKa is observed in micellar media due to the difference in the partition of acidic and basic forms of the solutes. A model has been developed to determine KPH and KP- from the pKa shifts observed. The values obtained by this pKa shift modeling method and those from self-diffusion coefficient measurements are in good agreement. The acidic form of C8C is incorporated to a larger extent into the Brij 58 micelles than the acidic form of C8T, whereas the opposite trend is observed for the basic forms. Both the acidic and basic forms of C8T are more easily incorporated into Brij 58 micelles than into Triton X-100 micelles. The influence of the structure of the polar head on the solubilization properties is demonstrated. Moreover, evidence for the localization of the solutes in the micelles is obtained from the comparison of the partition coefficients and from 1H NMR data.