P-31 NMR first spectral moment study of the partial magnetic orientation of phospholipid membranes

Structural data can be obtained on proteins inserted in magnetically orient ed phospholipid membranes such as bicelles, which ave most often made of a mixture of long and short chain phosphatidylcholine. Possible shapes for th ese magnetically oriented membranes have been postulated in the literature, such as discoidal structures with a thickness of one bilayer and with the short acyl chain phosphatidylcholine on the edges. In the present paper, a geometrical study of these oriented structures is done to determine the val idity of this model. The method used is based on the determination of the f irst spectral moment of solid-state P-31 nuclear magnetic resonance spectra . From this first moment, an order parameter is defined that allows a quant itative analysis of partially oriented spectra. The validity of this method is demonstrated in the present study for oriented samples made of DMPC, DM PC:DI-IPC, DMPC:DHPC:gramicidin A and adriamycin:cardiolipin.