|The IUCr is an International Scientific Union. Its objectives are to promote international cooperation in crystallography and to contribute to all aspects of crystallography, to promote international publication of crystallographic research, to facilitate standardization of methods, units, nomenclatures and symbols, and to form a focus for the relations of crystallography to other sciences.|
The properties of many technological important materials are intimately associated with the inherent disorder that exists in their crystal structures. There are numerous examples in the fields ranging from alloys, shape-memory alloys, ferroeletrics, fast ion conductors and semiconductors to high -Tc superconductors and even pharmaceuticals.
To understand these materials it is not sufficient to know their average unit-cell structure as revealed by Bragg scattering. It requires additionally knowledge of their local or nanoscale structure – information that can only be obtained from the diffuse scattering component of the total scattering. Obtaining such diffuse scattering data is now feasible for most crystalline materials, however interpreting and analysing the data remain problematic. There have been some attempts to make the analysis of diffuse scattering more routine and more readily available to a wider range of researchers but, in most cases the modelling still relies heavily on the experience of the investigator.
In view of the limitations of the current models, Welberry and Goossens [(2016). IUCrJ. 3, doi: 10.1107/S2052252516010629] decided to undertake a study to try to develop a new model that agrees more convincingly with observed data. Their paper re-examines results published by an earlier team and demonstrates how to analyse the diffuse scattering of experimental diffraction patterns.A related commentary to this paper exists: Sawa, (2016). IUCrJ. 3, doi: 10.1107/S2052252516013889
The Nobel Prizes in Physiology or Medicine, Physics and Chemistry have been announced this week. The Nobel Prize in Physiology or Medicine was awarded to Yoshinori Ohsumi "for his discoveries of mechanisms for autophagy". The Nobel Prize in Physics was divided, one half awarded to David J. Thouless, the other half jointly to F. Duncan M. Haldane and J. Michael Kosterlitz "for theoretical discoveries of topological phase transitions and topological phases of matter". The Nobel Prize in Chemistry was awarded jointly to Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard L. Feringa "for the design and synthesis of molecular machines".
Three of the Nobel Prize winners, Professor Yoshinori Ohsumi of the Tokyo Institute of Technology, Tokyo, Japan; Sir J. Fraser Stoddart of Northwestern University, Evanston, USA; and Professor Bernard L. Feringa of Groningen University, The Netherlands, have published in IUCr Journals.
|Click here to view articles by Yoshinori Ohsumi||Click here to view articles by Sir J. Fraser Stoddart||Click here to view articles by Bernard L. Feringa|
The 100th anniversary of powder diffraction is being celebrated in a blog by André Authier, Professor Emeritus at Université P. et M. Curie, Paris, France and former president of the IUCr. The blog describes the role of Paul Scherrer and Peter Debye in Göttingen, Germany, and Albert Hull in Schenectady, NY, USA, in discovering – independently – one of the most powerful and widely used methods for analysing matter. This centenary – along with the 50-year jubilee of the introduction of the Rietveld method – was recently commemorated at a Debye & Rietveld symposium in Amsterdam, The Netherlands. And at Nobel Prize time, it is interesting to note that it is 80 years since the Nobel Prize in Chemistry was awarded to Debye “for his contributions to our knowledge of molecular structure through his investigations on dipole moments and on the diffraction of X-rays and electrons in gases”.
Furthermore, the November 2016 issue of Acta Cryst. A will feature selected papers from DSE2015: 100 years of the Debye scattering equation, a workshop held at Cavalese, Italy in June 2015. The first article in this special issue, “Towards atomistic understanding of polymorphism in the solvothermal synthesis of ZrO2 nanoparticles” by Dippel et al., is now online.
It was the Softenon disaster that made the pharmaceutical industry fully aware of the importance of knowing the enantiomeric purity and chirality of drugs and their metabolites. This disaster involved the chiral drug Thalidomide that was sold in the 1950s as a racemate under various brand names such as Contergan and Softenon. It was shown in the early 1960s that only the R-enantiomer has the intended pharmaceutical effect and that the S-enantiomer, when the drug is used by pregnant females, may lead to serious miscarriages.
Until the 1950s, the chirality of a compound could only be determined by chemical methods. It was J. M. Bijvoet’s organic chemistry colleague, F. Kogl, working on the isolation of natural products and on a chirality-related cancer theory, who inspired Bijvoet to reinvestigate the possibility to directly determine the chirality of molecules such as natural and unnatural amino acids with X-ray diffraction techniques.
The first absolute structure determination of an organic compound, as proof of the principle, was carried out for sodium rubidium (+)-tartrate in 1950. This was a significant experimental feat at the time in view of the long exposure time required. Half a century later the absolute structure assignment to sodium rubidium (+)-tartrate was reaffirmed using state-of-the-art techniques.
With the advancement of the diffraction and computer hardware and the inclusion of anomalous dispersion contributions into the structure refinement software, it became customary to refine both enantiomeric models of a determined structure and keep the one with the lowest R-value as that representing the true absolute structure. Probability tests to determine the validity of the chosen absolute structure were often problematic; so work continued to improve the situation. A solution was finally resolved with the introduction of the Flack parameter. Absolute structure assignment turned out to be generally statistically reliable for compounds containing heavy atoms with significant resonant power. Unfortunately this was rarely the case for light atom structures containing only atoms of types O, N, C and H, yet absolute structure determination of light atom structures is of great interest in pharmaceutical research. To address the reliability issue a new approach was taken by Hooft et al. Subsequently, similar approaches, collectively addressed as post-refinement methods have been implemented in various software packages.
In a recently published paper Watkin, D. J. & Cooper, R. I. [(2016). Acta Cryst. B72, doi: 10.1107/S2052520616012890] describe the currently available techniques for absolute structure determination.
A revised impact factor for IUCrJ (5.316) has been released by Thomson Reuters.
This news follows on from a very successful launch for the journal in 2014, which saw many high profile papers published. IUCrJ is a fully open-access peer-reviewed journal which in its short life has attracted publications from many of the leading names in the field of crystallography and beyond.
The journal publishes high-profile articles on all aspects of the sciences and technologies supported by the IUCr, including emerging fields where structural results underpin the science reported in the article. IUCrJ is thus the natural home for high-quality structural science results. Chemists, biologists, physicists and material scientists are actively encouraged to report their structural studies in IUCrJ.
We would like to thank all the authors, reviewers and editors who have contributed to the success of the journal. Below we list the top ten most highly cited papers published in the journal so far.
Top ten most highly cited IUCrJ papers:
Neutron radiography is a non-destructive imaging technique, which provides information about the interior of an object with high spatial resolution by using neutron radiation. In contrast to X-ray radiography, neutron imaging is sensitive to some light elements such as hydrogen or lithium, while most heavy elements such as, for example, lead and aluminium can easily be penetrated. Consequently, this method is routinely applied in fields such as cultural heritage research, materials science, engineering, and geology, whenever X-rays fail to generate sufficient imaging contrast or lack penetration.
Nowadays, spatial resolution down to 50 microns are routinely obtained by means of neutron imaging, which are limited by the geometric resolution of the beamline and the resolution obtainable with neutron detectors. Several approaches have been proposed to investigate smaller structures. They are either based on the direct magnification of the image by focusing neutron optics or on the improvement of the detector resolution. However, if a direct resolution is not required, even smaller structures can be studied by a spatially resolved mapping of their scattering signature. A complementary imaging approach based on this principle is provided by neutron grating Interferometry (nGI).
Simply, nGI is an advanced neutron imaging method which allows the simultaneous recording of the neutron transmission image, the differential phase contrast image and the dark–field image.
The improving theoretical understanding of the nGI contrast mechanism has recently triggered the transition of nGI towards a quantitative method providing detailed information about the microstructure of the sample.
In a recently published paper in the Journal of Applied Crystallography, a group of scientists [Reimann et al., (2016). J. Appl. Cryst. 49, doi:10.1107/S1600576716011080] report on the setup and applications of a new neutron grating interferometer which has recently been implemented at the ANTARES imaging beamline at the Heinz Maier-Leibnitz Zentrum (MLZ).To learn more about ANTARES and to apply for beamtime visit this page.