Chaotropic anion-phosphatidylcholine membrane interactions: an ultra high field NMR study

NMR studies on the interaction of the linear chaotropic anions, SCN- and SeCN-, with sonicated egg phosphatidylcholine (EPC) vesicles have been carried out at field strengths up to 14.1 Tesla. At 600 MHz, both anions cause splitting or increased splitting of the choline N+(CH3)3, CH2N+ and O3POCH2 1H resonances with SeCN- being somewhat more effective in this action than is SCN-. No changes were observed in the glycerol CH2OP and CH2OCO 1H resonances and the phosphate 31P resonance of the headgroup region. The 13C spectrum was unchanged by the presence of the anions. After 18 h of exposure to the anion, the 1H resonance splittings but not the chemical shift values returned to those prior to anion exposure. Increasing the temperature of the vesicles decreased the anion-induced splitting, but, upon return to the beginning temperature, the chemical shifts did not return to their original values. The results are considered in terms of the 'molecular electrometer' model recently developed by Seelig and co-workers [1].