Search for content and authors
 

Sigma Cutoff - and What Lies Behind

Anna M. Makal 1,  Maksymilian Chruszcz 2,  Waldek Minor 2,  Krzysztof Woźniak 1

1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
2. University of Virginia, Molecular Physiology and Biophysics Dept. (UVA), 1300 Jefferson Park Av., Charlottesville, VA 22908, United States

Abstract

The I/sI cutoffs are commonly applied at all stages of crystallographic structure solution and refinement, as it is statistically justified to consider insignificant the intensities lower than three sI. The approach reduces actual dataset to the strong, well defined reflections, yielding better refinement statistics and shorter computational time. However, the weak signals may carry some information, especially in the case of charge density studies, where high resolution and, therefore, weaker reflections are essential for the proper structure refinement, and the number of refined parameters is great.

Expecting that some minute yet important effects may be lost due to the exclusion of weaker reflections, we decided to analyze the influence of applied I/sI cutoff on the series of multipole charge density refinements, conducted on a couple of datasets with sigma cutoffs of 4, 3, 2, 1 and 0 I/sI. The general quality of refinements measured by R-factors and residual density extrema improves slightly with the higher sigma cutoff applied. Interesting dependences of r(r) and Lap(r) vs I/sI cutoff are observed within the estimated errors range.
 

Legal notice
  • Legal notice:

    Copyright (c) Pielaszek Research, all rights reserved.
    The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
    In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/8537 must be provided.

 

Related papers
  1. What modern crystallography can add to pharmaceutical research?
  2. Physicochemical characterization of sunitinib and its impurities
  3. Experimental and theoretical charge density studies on a model analogue of vitamin D
  4. Redox processes of dithiolated tetraazamacrocyclic complexes of Ni(II) and Cu(II) in solution and immobilized on gold electrodes
  5. Charge Density Studies of Tetraazamacrocyclic Complexes of Copper(II) and Nickel(II)
  6. Fine-tuning of properties of bismacrocyclic dinuclear cyclidene receptors by N-methylation.

Presentation: poster at 18th Conference on Physical Organic Chemistry, Posters, by Anna M. Makal
See On-line Journal of 18th Conference on Physical Organic Chemistry

Submitted: 2006-07-04 16:16
Revised:   2009-06-07 00:44