Refined structure of 1,2-diacyl-P-O-ethylphosphatidylcholine bilayer membranes

1,2-diacyl-P-O-ethylphosphatidylcholines are synthetic cationic lipids that show some promising properties as nonviral DNA transfection agents. To gai n further insight in the effects of the additional ethyl group in the head, group region on the bilayer structure we systematically investigated a homo logous series of fully hydrated ethylphosphatidylcholines with linear satur ated chains (C14:0, C16:0, and C18:0) by small- and wide-angle X-ray diffra ction. Our data show that all of them form multilamellar vesicles with chai n interdigitated gel phases. Paying regard to the very importance of the li quid-crystalline phase in gene transfection, we applied the novel MCG metho d on high resolution X-ray diffraction data of the C16:0 derivative to be a ble to gain structural information on this phase. Comparison of this ethylp hosphatidylcholine with its parent compound, the unesterified phosphatidylc holine, revealed that the major difference in the liquid-crystalline phase is the significantly reduced water layer between the bilayers for the catio nic lipid. This may be one factor that contributes to the comparatively goo d DNA transfection efficiency of ethylphosphatidylcholines. (C) 2001 Elsevi er Science Ireland Ltd. All rights reserved.