Microstructure, order and fluidity of 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC8,9PC), a polymerizable lipid, by ESR and NMR.

Spectroscopic labeling studies of the gel phase and tubule phase of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) show that there is less chain mobility in the segments between the polar head-group and the diacetylene groups than in the segments between the diacetylenes and the terminal CH3 group. This lends support to the view that the diacetylene groups divide the molecule into two regions which have different packing arrangements and suggests that each region makes a separate contribution during the phase change of these lipids to form tubular microstructures. High-power deuterium NMR using deuterium-enriched 1,2-bis(hexadecanoyl)-sn-glycero-3-phosphocholine as a probe gives an order parameter of S = 0.46 in the hydrated tubule phase at 22 degrees C. ESR spectra of 5-, 12-, and 16-(4,4-dimethyl-3-oxazolidinyloxy or doxyl)stearic acid labels (DSAL) and 1-palmitoyl-2-(12-doxylstearoyl)phosphatidylcholine spin-label (PCSL) show that the fluidity for the lipid bilayers of the DC8,9PC tubule phase increases with distance of the doxyl group from the hydrophilic region of the bilayer. 5-DSAL, which is a probe of the phospholipid head group, gives an order parameter in the tubule phase of S = 0.38. Spectral evidence of ordering of the tubules by a magnetic field is observed by a change in the linewidth of the spectra.