MULTINUCLEAR MAGNETIC-RESONANCE STUDY OF THE COMPLEXATION OF LANTHANUM(III) BY D-GLUCITOL AND RIBITOL IN AQUEOUS-SOLUTION

A multinuclear magnetic resonance study (H-1, C-13, La-139) of the int eractions of La(III) with D-glucitol and ribitol in aqueous solution i s presented and is compared with recently published calorimetric data. The thermodynamic data were determined by La-139 NMR, and are in exce llent agreement with the calorimetric results: Delta H degrees = - 10. 3 +/- 1.2 kJ mol(-1) and Delta S degrees = - 25.7 +/- 3.9 J K-1 mol(-1 ) (La-139 NMR); Delta H degrees = - 10.2 kJ mol(-1) and Delta S degree s = - 25.8 J K-1 mol(-1) (calorimetry; from Rongere et al., op. cit.). A conformational analysis of D-glucitol shows that the complexation o f La(III) results from a 120 degrees rotation of the C-2-C-3 bond in t he most stable conformation of D-glucitol, thus providing three hydrox yl groups in a suitable spatial arrangement for the occupancy of the f irst coordination sphere of La(III) and the concurrent replacement of water molecules. (C) 1997 Elsevier Science Ltd.