DYNAMICS OF LIPID BILAYERS FROM COMPARATIVE-ANALYSIS OF H-2 AND C-13 NUCLEAR-MAGNETIC-RESONANCE RELAXATION DATA AS A FUNCTION OF FREQUENCY AND TEMPERATURE
Aa. Nevzorov et Mf. Brown, DYNAMICS OF LIPID BILAYERS FROM COMPARATIVE-ANALYSIS OF H-2 AND C-13 NUCLEAR-MAGNETIC-RESONANCE RELAXATION DATA AS A FUNCTION OF FREQUENCY AND TEMPERATURE, The Journal of chemical physics, 107(23), 1997, pp. 10288-10310
Analysis of the nuclear spin relaxation rates of lipid membranes provi
des a powerful means of studying the dynamics of these important biolo
gical representatives of soft matter. Here, temperature-and frequency-
dependent H-2 and C-13 nuclear magnetic resonance (NMR) relaxation rat
es for vesicles and multilamellar dispersions of 1,2-dimyristoyl-sn-gl
ycero-3-phosphocholine (DMPC) in the liquid-crystalline slate have bee
n fitted simultaneously to various dynamic models for different positi
ons of the acyl chains. The data include H-2 R-1Z rates (Zeeman order
of electric quadrupolar interaction) acquired at 12 external magnetic
field strengths from 0.382 to 14.6 T, corresponding to a frequency ran
ge from omega(D)/2 pi=2.50-95.3 NMz; and 2H R-1Q rates (quadrupolar or
der of electric quadrupolar interaction) at 15.3, 46.1, and 76.8 MHz.
Moreover, C-13 R-1Z data (Zeeman order of magnetic dipolar interaction
) for DMPC are included at six magnetic field strengths, ranging from
1.40 ro 17.6 T, thereby enabling extension of the frequency range to e
ffectively (omega(C)+omega(H))/2 pi=938.7 MHz. Use of the generalized
approach allows formulation of noncollective segmental and molecular d
iffusion models, as well as collective director fluctuation models, wh
ich were tested by fitting the H-2 R-1Z data at different frequencies
and temperatures (30 degrees C and 50 degrees C). The corresponding C-
13 relaxation rates were predicted theoretically and compared to exper
iment, thus allowing one to unify the C-13 and H-2 NMR data for bilaye
r lipids in the fluid state. A further new aspect is that the spectral
densities of motion have been explicitly calculated from the H-2 R-1Z
and R-1Q data at 40 degrees C. We conclude that the relaxation in flu
id membrane bilayers is governed predominantly by relatively slow moti
ons. which modulate the residual coupling remaining from faster local
motions (order fluctuations). Only the molecular diffusion model, incl
uding an additional slow motional process, and the membrane deformatio
n model describing three-dimensional collective fluctuations fit the H
-2 NMR data and predict the C-13 NMR data in the MHz range. Orientatio
nal correlation functions have been calculated, which emphasizes the i
mportance of NMR relaxation as a unique tool for investigating the dyn
amics of Lipid bilayers and biological membranes. (C) 1997 American In
stitute of Physics. [S0021-9606(97)01447-5].