Langs D A, Hauptman H A
Department of Structural Biology, Hauptman-Woodward Medical Research Institute, 700 Ellicott Street, Buffalo, NY 14203, USA.
Acta Crystallogr A. 2011 Sep;67(Pt 5):430-4. doi: 10.1107/S0108767311020137. Epub 2011 Jul 6.
A frustrating observation, based on an R(min) variance analysis within the `shake and bake' framework of direct methods phasing, is described. The variance of R(min) can on occasion identify large subsets of phases that have a significantly lower mean phase error than the entire direct methods phase set of otherwise unsuccessful phasing trials for which the overall phase error occasionally dips below 75 or 80°. This is the first time, other than for a handful of Σ1 phase indications in optimal situations, that a priori phase estimates have been attained for large numbers of E values, prior to solving the structure. Although the a priori variance of R(min) is a useful tool for identifying such phases, the a posteriori phase refinement shifts indicated by its minimum often prevent a successful convergence to the solution. Similar efforts to encourage solution convergences in the realm of real space have also been discouraging.
本文描述了一种令人沮丧的观察结果，该结果基于直接法相位测定“摇与烤”框架内的最小R值（R(min)）方差分析。R(min)的方差有时能够识别出大量相位子集，这些子集的平均相位误差明显低于整个直接法相位集，而对于其他未成功的相位测定试验，其整体相位误差偶尔会降至75°或80°以下。这是首次在求解结构之前，针对大量E值获得了先验相位估计，除了在最佳情况下少数几个Σ1相位指示外。尽管R(min)的先验方差是识别此类相位的有用工具，但其最小值所指示的后验相位精修偏移常常阻碍成功收敛到解。在实空间领域中为鼓励解收敛所做的类似努力也令人沮丧。
