31P-NMR signals from inner and outer surfaces of phospholipid membranes.

We showed earlier [ 1,2] that PMR spectroscopy of phospholipid membranes in the presence of paramagnetic ions makes it possible to distinguish between signals coming from the inner and outer surfaces of a membrane, since the signal from the N+(CH,), protons of the outer surface lecithin molecules is considerably shifted in comparison with the signal from the inner surface protons. As there are grounds for believing that paramagnetic cations will interact with the negatively charged lecithin phosphate groups, one would expect larger chemical-shift differences in using 3 ‘P-NMR spectroscOPY.