Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk, 630090, Russia.
J Phys Chem B. 2012 Jul 19;116(28):8139-44. doi: 10.1021/jp3038895. Epub 2012 Jul 6.
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.
研究了宽温域内自旋标记饱和 1,2-二棕榈酰-sn-甘油-3-磷酸胆碱（DPPC）和单不饱和 1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱（POPC）磷脂双层的喇曼散射和脉冲电子顺磁共振（EPR）。在 25 至 320 K 之间获得了 CH2 和 C-C 伸缩振动频率范围内的喇曼光谱。分析了对磷脂链间堆积、相互作用和链内扭转运动敏感的模式（2880 cm(-1)处不对称 CH2 伸缩模式）以及构象状态（1130 cm(-1)处 C-C 伸缩模式）。这些模式的喇曼强度强烈依赖于凝胶相中的温度。在饱和磷脂 DPPC 中，CH2 和 C-C 伸缩模式的喇曼强度的温度依赖性变化发生在大约 200-230 K 的相同温度附近。然而，在单不饱和 POPC 脂质中，1130 cm(-1)处 C-C 伸缩模式的温度依赖性在 170 K 附近显示出转变，不对称 CH2 伸缩模式转变的温度依赖性在 120 K 附近。对于嵌入脂质双层的 5-DOXYL-和 16-DOXYL-硬脂酸的自旋标记，电子自旋回波信号衰减的各向异性贡献被解释为纳秒随机摆动的结果。对于 DPPC 和 POPC，在高于 200 K 的温度下，摆动诱导的弛豫速率显着增加，这与喇曼散射数据一致。在高于 120 K 的温度下，POPC 脂质中观察到摆动诱导弛豫速率的明显增加，而 DPPC 脂质中的摆动诱导弛豫在 200 K 以下几乎与温度无关。在所提出的解释框架内，单不饱和脂质的双层结构包含有缺陷的、类似自由体积的位置，这些位置为磷脂酰基尾部在低温下的运动提供了自由。
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