ANOMALOUS X-RAY SCATTERING ON LIPID BICELLES

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 脂双核是由长链和短链磷脂在水中的二元和三元混合物形成的半径在几十纳米左右的扁平盘状胶束。这些双极体的一个有趣的性质是，它们能够在外部磁场下，在稀土离子(如Yb)存在的情况下部分定向。利用SPEAR3升级提供的显著改善的束流特性，特别是改善了束流亮度和稳定性，最近在BL4-2上成功地对马的脾铁蛋白进行了异常溶液散射实验的可行性测试。受这一结果的启发，并利用能量分辨漂移二极管探测器在荧光模式下精确测量吸收光谱，我们尝试测量了Yb离子在脂质双胶束悬浮液中的反常散射信号。大多数离子被认为与双极体的头基区密切相关，但它们主要是在圆盘的平坦双层区域还是在边缘尚不清楚。为了深入了解双原子束周围的离子分布，我们在Yb的L3吸收边(8944 EV)附近进行了反常的X射线散射实验。由于反常散射，我们检测到下面和吸收边的信号之间的差异，这在没有离子的样品中是不存在的。然而，由于并不是所有的离子都可以被假设为与二元胞直接相关，所以准确的分析变得复杂起来。我们目前正在对数据进行详细的建模和解释。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Lipid bicelles are flat disk-like micelles with a radius around several tens of nanometers formed by binary and tertiary mixtures of long- and short-chained phospholipids in water. One of the interesting properties of these bicelles is their ability to partially orient under an external magnetic field in the presence of lanthanide ions such as ytterbium. Taking advantage of the significantly improved beam characteristics provided by the SPEAR3 upgrade, in particular improved beam brightness and stability, the feasibility of anomalous solution scattering experiments at BL4-2 was recently tested successfully on horse spleen ferritin. Encouraged by this result and using energy-resolving drift diode detector to measure absorption spectra accurately in fluorescence mode, we made an attempt to measure the anomalous scattering signal from Ytterbium ions in a suspension of lipid bicelles. The majority of the ions are thought to be closely associated with the headgroup region of the bicelles but whether they are predominantly in the flat bilayer region of the disk or on the rim is not known. To gain some insight into the ion distribution around the bicelles we conducted anomalous x-ray scattering experiments near the L3 absorption edge (8944eV) of ytterbium. We detected a difference between the signal below and at the absorption edge due to the anomalous scattering, which was not present in the sample without the ions. The accurate analysis though is complicated by the fact that not all the ions can be assumed to be directly associated with the bicelles. We are currently working on the detailed modeling and interpretation of the data.