Unified picture for spin-lattice relaxation of lipid bilayers and biomembranes

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Abstract
The present study compares and interprets the 1H, 2H, and 13C spin-lattice (T1) relaxation times of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), in the liquid crystalline phase, in terms of models for the molecular dynamics of lipid bilayers. The 1H T1 times of the DPPC bilayer hydrocarbon region at two frequencies and 13C T1 data at seven frequencies, for which the relaxation is dipolar in origin, as well as the 2H T1 data at three frequencies, due to the quadrupolar interaction, can be unified and interpreted in terms of a collective model for order fluctuations. In normalizing the 13C T1 data to the 1H and 2H T1 values, a vibrationally corrected 13C–1H distance parameter of r0CH=1.14 Å has been assumed, rather than the equilibrium bond length of 1.09 Å. The analysis suggests that the behavior of the individual acyl chain segments of lipid bilayers, in the liquid crystalline phase, is similar to that of molecules in nematic fluids.