Infrared and 31P-NMR studies of the effect of Li+ and Ca2+ on phosphatidylserines

Infrared and \ub3\ub9P-NMR spectra of solid samples of Full-size image 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS) and 1.2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) have been recorded. Comparison of the spectra of the Na\u207a salts of these phospholipids with those of complexes formed with Li\u207a and Ca\ub2\u207a ions allows the characterization of conformational changes induced by complexation with Li\u207a and Ca\ub2\u207a. Ca\ub2\u207a forms tight, crystalline complexes with these phosphatidylserines (PS), irrespective of the degree of unsaturation in the hydrocarbon chains. In these PS-Ca\ub2\u207a complexes the torsion angles of the two P-O ester bonds exhibit the antiplanar-antiplanar conformation which is significantly different from the standard gauche-gauche conformation commonly found in phosphodiesters. In contrast, complexation with Li\u207a does not induce this conformational change in the phosphodiester group. It is shown that the degree of unsaturation in the hydrocarbon chains, and related to it, the cross-sectional area of the phospholipid or the surface charge density, determine the affinity of the phosphatidylserine for the metal ion. In general, the affinity of phosphatidylserines for both Li\u207a and Ca\ub2\u207a decreases with increasing unsaturation in the hydrocarbon chains or decreasing surface charge density; it is in the order DMPS > POPS > DOPS.Peer reviewed: YesNRC publication: Ye