Abstract：
The fluorescent marker Laurdan and its new derivative, C-Laurdan, have been investigated by means of theoretical calculations in a DOPC lipid bilayer membrane at room temperature, and a comparison is made with results from fluorescence experiments. Experimentally, the latter probe is known to have a higher sensitivity to the membrane polarity at the lipid headgroup region and has higher water solubility. Results from Molecular Dynamics (MD) simulations show that C-Laurdan is oriented with the carboxyl group toward the head of the membrane, with an angle of 50° between the molecular backbone and the normal to the bilayer, in contrast to the orientation of the Laurdan headgroup whose carbonyl group is oriented toward the polar regions of the membrane and which describes an angle of ca. 70-80° with the membrane normal. This contrast in orientation reflects the differences in transition dipole moment between the two probes and, in turn, the optical properties. QM/MM results of the probes show little differences for one- (OPA) and two-photon absorption (TPA) spectra, while the second harmonic generation (SHG) beta component is twice as large in Laurdan with respect to C-Laurdan probe. The fluorescence anisotropy decay analysis of the first excited state confirms that Laurdan has more rotational freedom in the DOPC membrane, while C-Laurdan experiences a higher hindrance, making it a better probe for lipid membrane phase recognition.
摘要：
荧光标记Laurdan及其新衍生物,C-Laurdan,已经通过室温下DOPC脂双层膜的理论计算进行了研究，并与荧光实验的结果进行了比较。实验上,已知后一种探针对脂质头基区域的膜极性具有更高的敏感性，并且具有更高的水溶性。分子动力学（MD）模拟结果表明，C-Laurdan的羧基朝向膜的头部，分子骨架和双层法线之间的角度为50°，与Laurdan头基的方向相反，后者的羰基朝向膜的极性区域，并且描述的角度为ca。70-80°与膜正常。这种方向上的对比反映了两个探针之间跃迁偶极矩的差异，反过来,光学特性。探针的QM/MM结果显示，单光子（OPA）和双光子吸收（TPA）光谱几乎没有差异，而相对于C-Laurdan探针，Laurdan的二次谐波产生（SHG）β分量是Laurdan的两倍。第一激发态的荧光各向异性衰减分析证实，Laurdan在DOPC膜中具有更多的旋转自由度，虽然C-Laurdan遇到了更高的障碍，使其成为更好的脂质膜相识别探针。
