Dittrich B, Strumpel M, Schäfer M, Spackman M A, Koritsánszky T
Chemistry M313, School of Biomedical, Biomolecular and Molecular Sciences, University of Western Australia, Crawley 6009, Australia.
Acta Crystallogr A. 2006 May;62(Pt 3):217-23. doi: 10.1107/S0108767306010336. Epub 2006 Apr 14.
The determination of molecular absolute configuration from an X-ray analysis for structures that contain only light elements is challenging owing to the weak anomalous dispersion signal. The achievable precision of the Flack x parameter for such structures is therefore limited, especially when the independent-atom model is employed. Invariom modelling can improve this situation. Invarioms are theoretically predicted pseudoatoms within the Hansen & Coppens multipole formalism. They are transferable from one molecule to another and provide generalized aspherical atomic form factors. It is shown that, by application of the invariom approach, the precision and standard uncertainty of the Flack x parameter and therefore the reliability of deducing molecular chirality in an absolute structure determination can be improved.
对于仅包含轻元素的结构，通过X射线分析确定分子绝对构型具有挑战性，这是因为反常色散信号较弱。因此，此类结构的弗拉克x参数所能达到的精度受到限制，尤其是在采用独立原子模型时。不变量建模可以改善这种情况。不变量是在汉森和科彭斯多极形式体系内理论预测的伪原子。它们可从一个分子转移到另一个分子，并提供广义的非球形原子形状因子。结果表明，通过应用不变量方法，可以提高弗拉克x参数的精度和标准不确定度，从而提高在绝对结构测定中推断分子手性的可靠性。
