Johnas S K J, Dittrich B, Meents A, Messerschmidt M, Weckert E F
HASYLAB at DESY, Hamburg, Germany.
Acta Crystallogr D Biol Crystallogr. 2009 Mar;65(Pt 3):284-93. doi: 10.1107/S0907444908040602. Epub 2009 Feb 20.
Two single-crystal X-ray diffraction data sets of cyclosporine A were measured to high resolution using synchrotron radiation at temperatures of 5 and 90 K. They allowed an accurate determination of its molecular and electronic structure. Three electron-density models based on pseudoatom scattering factors were compared in terms of derived bond topological properties and in terms of electron-density differences on a grid. In one model multipole parameters were freely refined, whereas in the other two models the density was built up from fixed database parameters from the invariom database and University at Buffalo Databank. The data quality not only allowed benchmarking of the quality of both databases with the refined density, but also judgement of the feasibility of a multipole refinement of a larger oligopeptide structure such as cyclosporine A. Both databases performed equally well and reproduced the experimentally determined charge density satisfactorily.
利用同步辐射在5K和90K温度下测量了两个环孢菌素A的单晶X射线衍射数据集，分辨率很高。这些数据集使得能够准确确定其分子和电子结构。基于赝原子散射因子的三个电子密度模型在导出的键拓扑性质以及网格上的电子密度差异方面进行了比较。在一个模型中，多极参数被自由精修，而在另外两个模型中，密度是根据来自invariom数据库和布法罗大学数据库的固定数据库参数构建的。数据质量不仅允许用精修后的密度对两个数据库的质量进行基准测试，还能判断对更大的寡肽结构（如环孢菌素A）进行多极精修的可行性。两个数据库表现同样出色，令人满意地再现了实验测定的电荷密度。
