Aa. Nevzorov et al., CORRELATION-FUNCTIONS FOR LIPID-MEMBRANE DYNAMICS OBTAINED FROM NMR-SPECTROSCOPY, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 55(3), 1997, pp. 3276-3282
Nuclear magnetic resonance (NMR) studies of the spin relaxation of lip
id membranes provide a powerful tool for investigating the dynamics of
these important biological structural elements. Here spectral densiti
es of motion for various dynamical models have been fitted to H-2 spin
-lattice relaxation rates' (R(1Z)) measured for vesicles for 1,2-dimyr
istoyl-sn-glycero-3-phosphocholine, in the liquid-crystalline state, o
ver a broad frequency range (2.59-95.3 MHz; total of 15 magnetic-field
strengths). Moreover, the corresponding C-13 R(1Z) values predicted f
rom the models have been compared to experiment from 15.0 to 151 MHz,
thereby enabling unification of the NMR relaxation data for bilayer li
pids. A molecular diffusion model or alternatively a three-dimensional
collective fluctuation model describes best the 2H and C-13 R(1Z) dat
a. To emphasize the universality of this approach, the models have als
o been fitted to C-13 R(1Z) data for vesicles of 1,2-dipalmitoyl-sn-gl
ycero-3-phosphocholine (15.0-151 MHz; eight magnetic field strengths),
and the H-2 R(1Z) values for the corresponding multilamellar dispersi
ons theoretically predicted. Correlation functions have been calculate
d for the lipid reorientations from the analysis of NMR relaxation dat
a. The results suggest that slower motions are predominant in the low
to mid megahertz range due to noncollective molecular motions or therm
al collective excitations, whereas the bilayer interior corresponds to
liquid hydrocarbon. The reorientational correlation functions derived
from NMR spectroscopy are compared to recent molecular-dynamics simul
ations of bilayer lipids in the fluid phase.