Miloudi Hlaïbi

A 13C AND 183W NMR STUDY OF D-GLYCERO-D-GULO-HEPTONIC ACID AS A MULTISITE LIGAND IN TUNGSTATE COMPLEXES

Abstract The formation of complexes ( x , y , z ) between x tungstate ions, y d -glycero- d -gulo- heptonate ions, and z protons was studied in aqueous solution by 13 C and 183 W NMR spectroscopy. The overall equilibrium constant for the complex-forming reaction was obtained by a competition method, showing that a (2,2,2) species prevails at pH 4–5. Depending on the pH, various species are formed that involve chelating oxygen atoms originating from hydroxyl groups only, or from the carboxyl and the α-hydroxyl groups. In acidic medium, three types of complexes are formed: a (2,1,2) complex at the arabino site (O-4,5,6,7), two complexes at the O-1,2 site which have either (1,2,2) or (2,2,2) compositions, and a mixed 5:2 complex involving O-1,2,4,5,6,7 of each ligand. In alkaline medium, the carboxylate group is not involved in chelation and a single (2,1,1) complex of the pentadentate ligand (O-2,3,4,5,6) was characterized.

Process of Facilitated Extraction of Vanadium Ions through Supported Liquid Membranes: Parameters and Mechanism

To conduct experiments related to the facilitated extraction phenomenon of vanadium ions (), three supported liquid membranes (SLMs) were prepared, each containing 0.01 M of methyl cholate (MC), resorcinarene (RESO), or trioctylamine (TOA) as extractive agents. Kinetic and thermodynamic models were developed, based on the interaction of the substrate () with the extractive agent T and the diffusion of the formed entity (TS) through the membrane. The experimental results verify the models, and to determine, macroscopic parameters, permeabilities (P) and initial fluxes (), and microscopic parameters, association constants () and apparent diffusion coefficients () related to formed entities (TS) and their diffusion through the membrane organic phase. The experimental results indicate that the mechanism on the migration of the ions through the membrane organic phase is based on the successive jumps of substrate, from one site to another of the extractive agent. To explain these results and understand the mechanism, we studied influence of temperature factor, and we determined activation parameters (, , and ). The results show that this extraction phenomenon is governed by a structural term. Therefore, the membrane performance changes according to nature and structure of the association site presented by each of extractive agents.