NMR study of the complexation of D-gulonic acid with tungsten(VI) and molybdenum(VI).
By using multinuclear (1H, 13C, 17O, 95Mo, 183W) magnetic resonance spectroscopy (1D and 2D), D-gulonic acid is found to form ten and seven complexes, respectively, with tungsten(VI) and molybdenum(VI), in aqueous solution, depending on pH and metal-ligand molar ratios. Two isomeric 1:2 (metal-ligand) complexes involving the carboxylate and the adjacent OH group are present in the pH range 2-9. At intermediate and high pH, molybdate forms a 2:1 tetradentate complex involving the four secondary hydroxyl groups, whereas tungstate forms one 2:1 terdentate species. At low and intermediate pH values, three 2:1 complexes are found for both metals, involving the carboxylate group and three secondary hydroxyl groups, as well as a 5:2 species involving the carboxylate group and all the secondary hydroxyl groups; the concentration of this species increases in time mainly at the expense of 2:1 and 1:2 complexes. Tungstate can also form two additional species, probably a 5:2 species involving the carboxylate group and all the hydroxyl groups, and a 2:1 pentadentate species involving the carboxylate group and all the secondary hydroxyl groups. In alkaline solutions, tungstate is able to form an additional 2:1 pentadentate complex involving all the hydroxyl groups.
Luísa Ramos
M
M
Department of Chemistry, University of Coimbra, Portugal.
Caldeira
M M
MM
Gil
V M
VM
D002236:Carbohydrate Conformation; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008982:Molybdenum / Q000737:chemistry*; D009994:Osmolar Concentration; D012996:Solutions; D013400:Sugar Acids / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry*; D014867:Water
D008024:Ligands; D012996:Solutions; D013400:Sugar Acids; D014867:Water; C015252:gulonic acid; D008982:Molybdenum; D014414:Tungsten