Electron paramagnetic resonance and Nuclear Magnetic Resonance studies of Lipid-Water systems

The MnII-lecithin aqueous dispersion has been investigated by means of e.p.r. spectra and of nuclear relaxation rates of water protons. Three different cases have been studied, namely (a) the integral system having only external MnII ions, (b) sonicated dispersions with MnII ions inserted in the vesicles and (c) the vesicles having only internal Mn II ions. A relaxation model has been proposed which takes into account the existence of a randomly distributed electron spin relaxation time and its effect on the nuclear relaxation rates. The relevance of metal-lipid interactions has been emphasised. The structural and dynamic features of the system investigated have been interpreted by the combined analysis of the e.p.r. lineshapes and of the paramagnetic contributions 1/T1p and 1/T 2p to the water proton relaxation rates.