POTENTIOMETRIC, LUMINESCENCE AND NMR-STUDY OF THE INTERACTION OF EU-III WITH GLYCERYL PHOSPHATES

Complexation of europium(III) with glyceryl-1- and -2-phosphates has b een studied by metal ion luminescence,H-1 and C-13 NMR spectroscopy an d potentiometry. From the luminescence and NMR studies, the formation of a 1:1 inner-sphere complex, in which the glyceryl phosphate is dire ctly bound to the metal, is confirmed. Similar apparent binding consta nts at pH 2 were obtained by the three methods. Values obtained by NMR at pH 2 are 53 M(-1) and 12 M(-1) for glyceryl-1- and -2-phosphate, r espectively. By comparison with literature data on related systems it is suggested that the ligands bind through the phosphate group. To obt ain structural information from the NMR data, complexation has also be en studied with the lanthanide ions Dy(III), Er(III) and Gd(III) using both chemical shift and relaxation data. From this, metal-proton dist ance ratios have been calculated. Comparison of H-1 and C-13 NMR Spect ral data in the presence of paramagnetic lanthanides suggests conforma tional equilibria in the solutions. From the potentiometric studies, g lobal formation constants have been determined, and speciation diagram s obtained over the pH range 1.5 less than or equal to pH less than or equal to 7.0 for ligand/metal ratios of 1 and 30. Implications of the se results on lanthanide induced fusion of phospholipid membranes are discussed. Copyright (C) 1996 Elsevier Science Ltd