Acta Crystallographica Section A

Foundations of Crystallography

Volume 63, Part 2 (March 2007)

Cover illustration: The molecular form of the guanosine-5'-phosphate tetramer [Zimmerman (1976). J. Mol. Biol. 106, 663-672] has vertices at points of a cubic lattice with parameter a defined by the distance of O6 from the centre. The height is H = 2a and the basis a square scaled by a factor 6 from the central hole. Another square, scaled by 3 [square root]

2 and turned by 45°, separates phosphates and bases. The indices of the molecular forms are indicated. Courtesy of A. Janner.

lead articles
research papers
letters to the editor
international union of crystallography

lead articles

Acta Cryst. (2007). A63, 87-107 [ doi:10.1107/S010876730605570X ]

Diffraction with a coherent X-ray beam: dynamics and imaging

F. Livet

Synopsis: Techniques for coherent X-ray scattering measurements are detailed. Applications in the study of the dynamics of fluctuations and in lensless high-resolution imaging are described.

Online 15 February 2007

research papers

Acta Cryst. (2007). A63, 108-125 [ doi:10.1107/S0108767306053748 ]

On the application of an experimental multipolar pseudo-atom library for accurate refinement of small-molecule and protein crystal structures

B. Zarychta, V. Pichon-Pesme, B. Guillot, C. Lecomte and C. Jelsch

Synopsis: A library describing the precise charge density of all chemical groups present in proteins has been developed from the charge-density analysis of several peptide crystals.

Online 15 February 2007

Acta Cryst. (2007). A63, 126-130 [ doi:10.1107/S0108767306055310 ]

The concept of resolution in the domain of rotations

S. Trapani, X. Siebert and J. Navaza

Synopsis: A more economic distortion-free FFT sampling of two-dimensional sections of functions defined on the rotation domain is presented.

Online 15 February 2007

Acta Cryst. (2007). A63, 131-134 [ doi:10.1107/S0108767306054158 ]

A direct phasing method based on the origin-free modulus sum function and the FFT algorithm. XII

J. Rius, A. Crespi and X. Torrelles

Synopsis: A new phase refinement procedure maximizing the origin-free modulus sum function with the FFT algorithm is described so that no explicit use is made of the triple phase relationships. It is general for all space groups and especially effective for low-symmetry ones.

Online 15 February 2007

Acta Cryst. (2007). A63, 135-145 [ doi:10.1107/S0108767306054286 ]

Are intramolecular dynamic electron correlation effects detectable in X-ray diffraction experiments on molecular crystals?

I. Bytheway, G. Chandler, B. Figgis and D. Jayatilaka

Synopsis: Theoretical structure factors for a range of small molecules are calculated with and without dynamic electron correlation, to establish the size of these effects, and if they can be detected in experimental measurements.

Online 15 February 2007

Acta Cryst. (2007). A63, 146-155 [ doi:10.1107/S0108767306052809 ]

The highest reflection intensity in a resolution shell

M. Bochtler and G. Chojnowski

Synopsis: The Gumbel-Fisher-Tippett (GFT) extreme-value analysis is applied to evaluate the distribution, expectation value and standard deviation of the intensity J_a of the strongest reflection in a resolution shell.

Online 15 February 2007

Acta Cryst. (2007). A63, 156-163 [ doi:10.1107/S0108767306055991 ]

Ab initio neutron crystallography by the charge flipping method

G. Oszlányi and A. Süto

Synopsis: It is demonstrated that the dual-space charge flipping algorithm is able to solve structures using neutron diffraction data alone. For this purpose, its band flipping variant was introduced which reverses the sign of scattering density only in a zero-centred band. While band flipping is absolutely necessary for developing negative densities, it is the `basic + band' combination of algorithm variants that works most efficiently.

Online 15 February 2007

Acta Cryst. (2007). A63, 164-171 [ doi:10.1107/S0108767307000621 ]

An integer minimal principle and triplet sieve method for phasing centrosymmetric structures

A. B. Smith, H. Xu and N. V. Sahinidis

Synopsis: A reliable integer minimal principle model for phasing in all centrosymmetric space groups is presented. It dramatically reduces the number of cycles required to phase a selection of structures in the SnB framework.

Online 15 February 2007

Acta Cryst. (2007). A63, 172-176 [ doi:10.1107/S0108767307002723 ]

Coherent coexistence of nanodiamonds and carbon onions in icosahedral core-shell particles

V. Ya. Shevchenko, A. E. Madison and A. L. Mackay

Synopsis: In icosahedral carbon nanoparticles, the diamond-like core can undergo a reversible topological transition into and coexist coherently with the onion shells.

Online 15 February 2007

Acta Cryst. (2007). A63, 177-185 [ doi:10.1107/S0108767306056467 ]

Hybrid quasiperiodic-periodic structures constructed by projection in two stages

S. I. Ben-Abraham and A. Quandt

Synopsis: Hybrid quasiperiodic-periodic structures (octagonal, dodecagonal and pentagonal/decagonal) are constructed by cut and projection in two stages.

Online 15 February 2007

Acta Cryst. (2007). A63, 186-197 [ doi:10.1107/S0108767306052421 ]

Tangled (up in) cubes

S. T. Hyde and G. E. Schröder-Turk

Synopsis: Tangled cubes contain cycles of edges that form links and knots, yet retain the topology of the edge-net of the cube. The simplest tangled cubes are derived, constrained to have cycles of maximal length eight. Five left-handed and right-handed pairs result. All these examples wrap on the genus-one torus, forming a {6,3} tiling with four hexagonal faces in the torus.

Online 15 February 2007