Aluminum binding to phosphatidylcholine lipid bilayer membranes:: 27Al and 31P NMR spectroscopic studies

(27)AI and P-31 nuclear magnetic resonance (NMR) spectroscopies were used to investigate aluminum interactions at pH 3.4 C with model membranes composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). A solution state Al-27 NMR difference assay was developed to quantify aluminum binding to POPC multilamellar vesicles (MLVs). Corresponding one-dimensional (1D) fast magic angle spinning (MAS) (PNMR)-P-31 spectra showed that aluminum induced the appearance of two new isotropic resonances for POPC shifted to -6.4 ppm and -9.6 ppm upfield relative to, and in slow exchange with, the control resonance at -0.6 ppm. Correlation of the Al-27 and P-31 NMR binding data revealed a 1:2 aluminum:phospholipid stoichiometry in the aluminum-bound complex at -9.6 ppm and a 1: 1 aluminum: phospholipid stoichiometry in that at -6.4 ppm. Slow MAS 31 p NMR spectra demonstrated shifts in the anisotropic chemical shift tensor components of the aluminum-bound POPC consistent with a close coordination of aluminum with phosphorus. A model of the aluminum-bis-phospholipid complex is proposed on the basis of these findings. (C) 2004 Elsevier Ireland Ltd. All rights reserved.