. 2004 Apr;60(Pt 2):155-62. doi: 10.1107/S0108768104003325.Epub 2004 Mar 18.
The surprisingly elusive crystal structure of sodium metabisulfite
Kay L Carter 1, Tasneem A Siddiquee, Kristen L Murphy, Dennis W Bennett
Affiliations expand
PMID: 15017087
DOI: 10.1107/S0108768104003325
The crystal structure of Na2S2O5, a simple and common ionic compound, is reported here for the first time. The crystals form non-merohedral twins, with the twin domains related by a twofold axis which bisects the angle between the a and c axes of each unit cell. The structure was determined from a single-crystal fragment of a twinned crystal that had undergone cleavage along the twin boundary. In addition to the problems associated with twinning, space-group determination proved difficult as well, with the structure initially determined in the P2(1) space group appearing to be disordered with two rotational conformers of the metabisulfite ion occupying equivalent sites in the lattice. An analysis at low temperature provided new weak reflections which were inconsistent with the original unit cell, but indexed to the correct unit cell, allowing for space group and crystal structure determination. The apparent structure, which appeared disordered in P2(1), seems to have resulted from an apparently fortuitous superposition of two conformationally inequivalent S2O5(2-) anions in the asymmetric unit of the correct structure in the P2(1)/n space group. The metabisulfite ions in this structure do not adopt the C(s) geometry observed in previously determined crystal structures containing S2O5(2-). The structures of both ions in the asymmetric unit are effectively conformational mirror images of one another with two of the O atoms on each S atom in the ion approaching an eclipsed geometry. This observation provides further evidence that the structures of sulfur-oxy anions in the solid state are dictated mainly by interionic coulombic forces rather than by intraionic bonding interactions
https://pubmed.ncbi.nlm.nih.gov/15017087/
The apparent structure, which appeared disordered in P2(1), seems to have resulted from an apparently fortuitous superposition of two conformationally inequivalent S2O5(2-) anions in the asymmetric unit of the correct structure in the P2(1)/n space group.
https://pubmed.ncbi.nlm.nih.gov/15017087/
Acta Crystallogr D Biol Crystallogr
. 2004 Jun;60(Pt 6):1040-7.doi: 10.1107/S0907444904006948. Epub 2004 May 21.
Structural determination of a partially hemihedrally twinned actin crystal
Lakshmanan Govindasamy 1, Robbie Reutzel, Mavis Agbandje-McKenna, Robert McKenna
Affiliations expand
PMID: 15159563
DOI: 10.1107/S0907444904006948
Abstract
An orthorhombic actin crystal (space group P2(1)2(1)2(1), unit-cell parameters a = 101.6, b = 103.0, c = 127.0 angstroms) was converted into a partially hemihedrally twinned tetragonal crystal (space group P4(3), unit-cell parameters a = b = 101.5, c = 104.2 angstroms) by induced condensation. This condensation (decrease in the c axis) was caused by the flash-freezing of the crystal, with 30% PEG 400 as a cryoprotectant, prior to data collection. Diffraction data for the twinned tetragonal crystal were collected at 100 K to 3.0 angstroms resolution (99.8% completeness with an Rsym of 8.1%) using synchrotron radiation. The hemihedral twinning of the data was observed by self-rotation function analysis and was determined to have a partial twin fraction of 0.376 from intensity statistics. The structure, with two actin molecules in the crystallographic asymmetric unit, was determined by molecular-replacement methods and refined to an R factor of 0.193. As a consequence of the crystal lattice transformation from the orthorhombic P2(1)2(1)2(1) to the tetragonal P4(3) space group, actin-actin contacts were rearranged and an inter-actin dimer disulfide bond (Cys374) observed in the orthorhombic crystal form was broken in the tetragonal crystal form.
Copyright 2004 International Union of Crystallography
https://pubmed.ncbi.nlm.nih.gov/15159563/
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