Reactivity of Al(III) with membrane phospholipids: A NMR approach

The complexes Al(acac)3 (1) (acac = 2,4-pentanedionate) and Al(malt)3 (malt = 3-hydroxy-2-methyl-4-pyronate) (2) react with DL-?- dipalmitoylphosphatidylcholine (DPPC) under a 1:1 molar ratio in CDCl3 at 37°C, as shown by the substantial release of ligands (20-50%) from the metal coordination sphere (1H-NMR), by evident changes in the 1H-NMR spectrum of DPPC in the reaction mixture and by the appearance of a 31P-NMR signal due to metal-coordinated DPPC. 31P-NMR spectra reveal that both 1 and 2 also react with DPPC in water, in the presence of 1% Triton X-100 and Tris buffer. Under these conditions, 1 and 2 do not react with ghosts from human erythrocytes. On the contrary, the far less hydrolytically stable complex Al(lact)3 (lact = lactate) appears to be reactive under identical conditions, as shown by 31P-NMR spectra.