PMID: 3897353;Abstract:
Recent NMR relaxation studies of lipid bilayers and biomembranes are explained and briefly discussed. The results of both 2H and 13C NMR investigations suggest that, in addition to rapid local fluctuations of the hydrocarbon chains, slower, more collective motions of the bilayer exist. When the influence of the latter is recognized and properly accounted for, the contribution from local motions can be used to estimate a value for the microviscosity of the bilayer which corresponds to that of a simple n-paraffinic liquid. In general, the dynamic behavior of lipid bilayers as studied by NMR appears quite similar to that of simpler liquid crystals. © 1985.
PMID: 12390036;Abstract:
Quasi-elastic neutron scattering (QENS) was employed to study the molecular dynamics of three structurally related sterols, namely, cholesterol, lanosterol, and ergosterol. Oriented bilayers of dipalmitoylphosphatidylcholine (DPPC) were investigated at 40 mol % sterol content and at three temperatures (20, 36, and 50 °C) for two energy resolutions. Data analysis was concentrated on a direct comparison of the out-of-plane and the in-plane high-frequency motions of the three sterols in terms of their rates and amplitudes. The (spatially restricted) diffusive motion of the three sterols in the two directions was characterized by diffusion constants in the range of (5-30) x 10-12 m2 s-1, with a significantly faster rate of diffusion along the membrane normal, resulting in a diffusional anisotropy, Da. At low temperature (20 °C), cholesterol showed the highest value (Da = 4.5), while lanosterol gave the lowest one (Da = 2.0). At high temperature (50 °C), ergosterol diffusion had the highest diffusion anisotropy (Da = 2.0) compared to lanosterol (Da = 1.8) and cholesterol (Da = 1.6). Most interestingly, cholesterol showed at all three temperatures an amplitude of its out-of-plane-motion of 1.0-1.1 nm, more than a factor of 3 higher than measured for the other two sterols. This finding suggests that the short alkyl chain of the cholesterol molecule may cross at high frequency the bilayer midplane, while the other two sterols remain confined within the geometrical limits of each monolayer leaflet. The results provide an example of how slight structural alterations of sterols can affect their molecular dynamics in bilayers, which in turn may be relevant to the membrane micromechanical properties.
Abstract:
We describe here the design and construction of a modern, state-of-the-art nuclear magnetic resonance (NMR) field-cycling instrument. Fourier transform NMR spectra of both liquid and solid samples can be measured, and spin-lattice relaxation times (T1Z) investigated over a broad range of magnetic field strengths ranging from 0 to 2 T. The instrument is based upon an existing personal computer-based NMR spectrometer [C. Job, R. M. Pearson, and M. F. Brown, Rev. Sci. Instrum. 65, 3354 (1994)] which has been expanded into a fully computer-controlled field-cycling instrument. The magnetic field cycling is accomplished electronically by utilizing fast switching thyristors and a storage capacitor based on the Redfield energy storage concept. Unique aspects of the design include the field-cycling magnet, which can reach fields as high as 2 T; the personal computer-based NMR spectrometer and associated waveform electronics; and the use of a commercially available pulse width modulation switching current amplifier, having low internal power dissipation and a fast current settling time. Using this new technology T1Z relaxation times as short as 1 ms can be readily measured. © 1996 American Institute of Physics.
