Binary phospholipid bilayers composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine and 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) were studied by Raman spectroscopy and differential scanning calorimetry (DSC). We examined features in Raman scattering spectra that are sensitive to the lipid phase and, therefore, could indicate the phase coexistence. It was found that the low-frequency half-width of half-maximum (LHWHM) of the 2850 cm−1 Raman line, corresponding to the symmetric CH2 stretching vibrations, unequivocally reveals the coexisting phospholipids in ordered and disordered conformational states, which correspond to ordered and disordered phases coexistence, in the DPPC mole concentration range from 0.4 to 0.9. The phase coexistence in this concentration range was supported by the particular concentration behavior of the ratio between the intensities of the 2880 cm−1 antisymmetric CH2 vibration line and the 2850 cm−1 symmetric one. It was also shown that the spectral shape of the 1300 cm−1 Raman line, corresponding to the CH2 twisting vibrations, is a good indicator for the phase state and phase coexistence in the phospholipid bilayers. Comparison with the DSC curves confirmed that in the DPPC mole concentration range from 0.4 to 0.9, the two phase transition peaks are observed in DSC curve, those positions are independent of the DPPC concentration. The outcome of the study is the robust label-free contactless approach for the detection of the lipid phase separation, which can be realized with the micrometer resolution.

中文翻译：

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EXPRESS：二元磷脂双分子层中相共存的拉曼光谱研究

通过拉曼光谱和差示扫描量热法 (DSC) 研究了由 1,2-dioleoyl-sn-glycero-3-phosphocholine 和 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) 组成的二元磷脂双层。我们检查了对脂质相敏感的拉曼散射光谱中的特征，因此可以表明相共存。发现 2850 cm-1 拉曼谱线的低频半峰宽 (LHWHM)，对应于对称的 CH2 伸缩振动，明确揭示了共存的有序和无序构象状态的磷脂，其对应于有序相和无序相共存，在 DPPC 摩尔浓度范围从 0.4 到 0.9。2880 cm-1 反对称 CH2 振动线和 2850 cm-1 对称振动线的强度之比的特定浓度行为支持了该浓度范围内的相共存。还表明，对应于 CH2 扭曲振动的 1300 cm-1 拉曼线的光谱形状是磷脂双层中相态和相共存的良好指标。与DSC曲线比较证实，在DPPC摩尔浓度范围为0.4-0.9时，DSC曲线中观察到两个相变峰，这些位置与DPPC浓度无关。该研究的结果是用于检测脂质相分离的强大的无标记非接触方法，该方法可以通过微米分辨率实现。