Low-temperature dynamical and structural properties of saturated and monounsaturated phospholipid bilayers revealed by Raman and spin-label EPR spectroscopy.
The Raman scattering and pulsed electron paramagnetic resonance (EPR) of spin-labeled saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and monounsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) phospholipid bilayers in a wide temperature range were studied. Raman spectra in the frequency range of CH2 and C-C stretching vibrations were obtained between 25 and 320 K. The modes sensitive to phospholipid interchain packing, interaction, and intrachain torsional motions (asymmetric CH2 stretching mode at 2880 cm(-1)) as well as conformational states (C-C stretching mode at 1130 cm(-1)) were analyzed. The Raman intensities of these modes significantly depend on the temperature in the gel phase. In the saturated phospholipid DPPC, changes in the temperature dependence of Raman intensities occur near the same temperature for the CH2 and C-C stretching modes, which is approximately 200-230 K. However, in monounsaturated POPC lipids, the temperature dependence for the C-C stretching mode at 1130 cm(-1) reveals a transition near 170 K, and the temperature dependence for the asymmetric CH2 stretching mode transition was near 120 K. For spin-labeled 5-DOXYL- and 16-DOXYL-stearic acids embedded into lipid bilayers, the anisotropic contribution to the electron spin-echo signal decays was interpreted as a result of nanosecond stochastic librations. The decay rates increased remarkably at temperatures above 200 K for DPPC and POPC, which is consistent with the Raman scattering data. A noticeable increase in the libration-induced relaxation rate was observed in POPC lipids above 120 K, and libration-induced relaxation was nearly temperature-independent in DPPC lipids up to 200 K. In the framework of the suggested interpretation, the bilayer structure of monounsaturated lipids contains defective, free volume-like places that provide freedom for phospholipid acyl-tail motions at low temperatures.
Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk, 630090, Russia. lab21@iae.nsk.su
N V
NV
Surovtsev
N V
NV
Ivanisenko
K Yu
KY
Kirillov
S A
SA
Dzuba
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D008051:Lipid Bilayers / Q000737:chemistry*; D010712:Phosphatidic Acids / Q000737:chemistry*; D013113:Spin Labels
C103238:1-palmitoyl-2-oleoyl-glycero-3-phosphatidic acid; D008051:Lipid Bilayers; D010712:Phosphatidic Acids; D013113:Spin Labels; D015060:1,2-Dipalmitoylphosphatidylcholine