Interactions of aluminium(III) with glycerolphosphates and glycerophosphorylcholine

Abstract

The complexation of aluminium(III) with glycerol-1-phosphate (G1P) and glycerol-2-phosphate (G2P) in aqueous solutions has been studied as a function of pH, by pH-potentiometry, 31P NMR spectroscopy and ESI mass spectrometry. Various mononuclear complexes (MLH 2 3+, MLH 2+, ML +, ML 2H, ML 2 −) and polynuclear species (M 3L 3H −1 2+, M 3L 2H − n ( n−5)− with n=5, 6, 7, M 2L 2H −1 + ) are formed in the system where the full protonated ligands are noted LH 2. NMR experiments clearly show that G1P and G2P already interact with Al(III) at pH 1. The potentiometric results are confirmed by ESI measurements and 31P NMR studies. No metal ion-induced deprotonation and coordination of the alcoholic-OH functions seem to occur during the complexation. The situation is very different for the glycerophosphorylcholine ligand (GPC ≡ LH). Only the complex ML 3+ is formed in aqueous solution with a relatively low formation constant (K=5 at 37 °C). This species is clearly identified in 31P and 27Al NMR spectra. The complexation study as a function of the temperature allowed us to determine the thermodynamic parameters of the complex formation. The complexation is not governed by the reaction enthalpy that is found to be positive but by the entropy that is largely positive.