Physical studies of phospholipids VIII. Nuclear magnetic resonance studies of diacyl- l-phosphatidylcholines (lecithins)

Abstract

Proton magnetic resonance spectra of anhydrous polycrystalline 1,2-distearoyl-phosphatidylcholine (lecithin) have been obtained at temperatures between 196° and 150°. The decrease of line width and second moment with increasing temperature indicates increasing rates and amplitudes of reorientation up to a sharp transition point. The motion is probably rotatory and oscillatory in nature, but with a wide distribution of correlation frequencies. The mesomorphic phase above the transition gives a narrow nuclear magnetic resonance absorption line corresponding with rapid molecular reorientation which is not isotropic. Similar spectra are found for egg yolk lecithin, and the discussion of molecular motion in phospholipids may therefore be relevant for the reorientations of many lipids in biological membranes. Preliminary studies of the influence of water ( 2H 2O) on the molecular motion of phospholipids are also described.