Acta Crystallographica Section AActa Crystallographica Section A: Foundations of Crystallography publishes papers reporting fundamental advances in all areas of crystallography in the broadest sense. The central themes are, on the one hand, experimental and theoretical studies of the properties and arrangements of atoms, ions and molecules in condensed matter, ideal or real, and of their symmetry and, on the other, the theoretical and experimental aspects of the various methods to determine these arrangements.Intensity statistics of Friedel opposites- June 17, 2008 A previous analysis of the average intensity and mean-square intensity difference of Friedel opposites, confined to the space group P1 Flack & Shmueli (2007). Acta Cryst. A63, 257265, is here extended to all the non-centrosymmetric space groups. The present analysis presumes purely non-centrosymmetric content of the unit cell. An important result of this study is that the average intensity and mean-square intensity difference of Friedel opposites have the same values for all the...http://scripts.iucr.org/cgi-bin/paper?sh5073 X-ray atomic orbital analysis. I. Quantum-mechanical and crystallographic framework of the method- June 17, 2008 The scattering unit of X-ray crystal structure analysis is changed from atoms to the subshell electrons by X-ray atomic orbital analysis (XAO). All the atoms in the unit cell are divided into groups of subshell electrons in the XAO analysis. Each subshell is treated as an independent pseudo-atom, which enables the atomic orbitals (AO's) and the electron population of each AO expressed as a linear combination of spdf orbitals in each subshell to be determined. When the environmental condition of.http://scripts.iucr.org/cgi-bin/paper?cn5011 Estimated H-atom anisotropic displacement parameters: a comparison between different methods and with neutron diffraction results- June 17, 2008 Anisotropic displacement parameters (ADPs) are compared for H atoms estimated using three recently described procedures, both among themselves and with neutron diffraction results. The results convincingly demonstrate that all methods are capable of giving excellent results for several benchmark systems and identify systematic discrepancies for several atom types. A revised and extended library of internal H-atom mean-square displacements is presented for use with Madsen's SHADE web server J....http://scripts.iucr.org/cgi-bin/paper?sh5076 Applications and properties of the Bijvoet intensity ratio- June 17, 2008 An empirical relationship of use in prediction and evaluation is established between the standard uncertainty of the Flack parameter and the Bijvoet intensity ratio. The expected value of this ratio may be calculated from the chemical composition of the compound and the X-ray wavelength. Structure analyses published with intensity data have allowed various properties of the Bijvoet intensity ratio to be studied. It is found that, although the Bijvoet intensity ratio has a strong dependence on...http://scripts.iucr.org/cgi-bin/paper?sh5074 Comparative architecture of octahedral protein cages. I. Indexed enclosing forms- June 17, 2008 The architectural elements of four protein cages (bacterio ferritin, human mitochondrial ferritin, sulfur oxygenase reductase and small heat-shock protein) are compared top-to-bottom. The starting points are polyhedra with octahedral symmetry 432 enclosing the cage and delimiting the central cavity, respectively, which have vertices at points of a species-dependent cubic form lattice. The approach is extended from the whole cage to axial-symmetric clusters down to polyhedral forms of single...http://scripts.iucr.org/cgi-bin/paper?sh5071 Comparative architecture of octahedral protein cages. II. Interplay between structural elements- June 17, 2008 In paper I Janner (2008). Acta Cryst. A64, 494502, the enclosing forms of the monomers of four octahedral holoenzymes (bacterio and mitochondrial ferritins, small heat-shock protein and sulfur oxygenase reductase) were derived, with vertices at points of a cubic lattice and indexed accordingly. The correspondence between vertices and neighboring residues allows a sequential ordering of the vertices within the polyline defined by the C atoms of the primary structure. The alignment of these...http://scripts.iucr.org/cgi-bin/paper?sh5072 Advanced structural inorganic chemistry. IUCr Texts on Crystallography No. 10. By Wai-Kee Li, Gong-Du Zhou and Thomas Chung Wai Mak. Oxford: Oxford Un- June 17, 2008http://scripts.iucr.org/cgi-bin/paper?pf0065 |