|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.|
In order to fulfill its roles to promote international cooperation in crystallography and to contribute to the advancement of crystallography in all its aspects the IUCr regularly sponsors symposia and workshops on topics relevant to crystallography. There is a well defined procedure that should be followed when applying for sponsorship. The rules can be found here.
Part of the condition of sponsorship includes the following
If you are organizing a meeting and wish to be considered for IUCr support please visit http://www.iucr.org/iucr/sponsorship/meetings.html
Dental burs are used extensively in dentistry to mechanically prepare tooth structures for restorations (fillings); dental burs can be made of stainless steel, diamond or tungsten carbide (WC) cemented with cobalt or nickel. Generally, dental burs come in different kinds and shapes. Each of these kinds of burs is used for a specific function when drilling into the crown of a tooth to create a cavity in which filling material is placed. Stainless steel burs are used if the cutting is pursued at speeds slower than 5000 rpm, while at high speeds diamond-coated burs are most efficient in carving the brittle enamel, and WC burs are most efficient in cutting dentin.
Little has been reported on the bur debris left behind in the teeth, and whether it poses potential health risks to patients. The bur debris can remain within the prepared tooth structure, or be ingested or inhaled, and, owing to their sharp edges, can become lodged in soft tissue. In one study, magnetic resonance images revealed the presence of dental bur artifacts in both second premolar areas of the mandible.
A group of scientists in Canada [Hedayat et al. (2016). J. Synchrotron Rad. 23, doi:10.1107/S1600577516002198] aimed to image dental bur debris under dental fillings, and allude to the potential health hazards that can be caused by this debris when left in direct contact with the biological surroundings, specifically when the debris is made of a non-biocompatible material.
Non-destructive high resolution micro-computed tomography using hard X-rays 05ID-2 beamline at the Canadian Light Source was used to image dental bur fragments under a composite resin dental filling. The bur’s cutting edges that produced the fragment were also chemically analysed. The technique revealed dental bur fragments of different sizes in different locations on the floor of the prepared surface of the teeth and under the filling, which places them in direct contact with the dentinal tubules and the dentinal fluid circulating within them. Dispersive X-ray spectroscopy elemental analysis of the dental bur edges revealed that the fragments were made of tungsten carbide-cobalt, which is bio-incompatible.
The amount of bur fragments found in the teeth is small, and it is uncertain if, or to what degree, this constitutes a biohazard to patients. Accordingly, further research is needed to investigate the effect of the non-biocompatible dental bur fragments.
A new definitive reference to the Cambridge Structural Database (CSD) has been published [Groom et al. (2016), Acta Cryst. B72, 171-179; doi:10.1107/S2052520616003954]. The article provides updated information on the use, development and future of this database.
In 2015 the number of entries in the CSD surpassed 800,000. This is twice the number of entries in the database less than a decade ago. Along with the significant number of new structures published per year, what has changed in the database is the complexity of the structures being published: the average number of atoms per structure and the average molecular weight have increased, and there has also been an increase in the proportion of structures that are polymeric or that have resolved disorder.
The database provides value in two distinct ways. The first simply relates to the aggregation and standardisation of structures and the second comes from the unique study of the collection of entries. Discoverability of data by chemists and biologists is enabled by establishing links to datasets from services such as ChemSpider and PubChem. Links from ChemSpider and PubChem have been established for over 52,000 compounds that could be reliably identified using the International Chemical Identifier Standard (InChI).
CSD community web services provide free access to the entire collection of individual structures. As well as these services there are a number of other avenues to explore and exploit the data, ranging from free lookup tools such as CellCheckSCD to advanced search, analysis and validation tools in the CSD-System. More specialist applications can be found in the CSD-Enterprise Suite.Although the CSD contains all published crystal structures, it has been estimated that only 15% of structures determined are ever published. Automatic links in software used during structure determination, the ease with which structures can be deposited, attribution of credit in the form of a DOI and continued demonstration of the value to science of depositing crystal structures may help close this gap.
An ANSTO Planetary Materials scientist has used the Australian Synchrotron to identify the structure of a new material that could be crucial in understanding the hydrological cycle on Titan, the largest moon of Saturn, and important in assessing its potential habitability.
Helen Maynard-Casely used the Powder Diffraction instrument at the Australian Synchrotron to determine the atomic structure of the new material, a co-crystal between benzene and ethane that forms at 90 Kelvin (-179.2 oC). The experiment was done in situ under cryogenic conditions similar to Titan [Maynard-Casely et al. (2016), IUCrJ, 3, doi: 10.1107/S2052252516002815]. The material, which is formed by molecules of benzene and ethane, had first been identified by her collaborators at the Jet Propulsion Laboratory in the United States using spectroscopy. "They had no way of knowing exactly what they had until the crystalline structure could be found," said Maynard-Casely.
Maynard-Casely went on to say, "Only the diffraction of X-rays, which interact with the electrons of this hydrogenous material, could provide information about the arrangement of atoms in a crystal lattice. The structure of the new material is based on the structure of pure benzene; with its framework stabilized by attraction between hydrogen atoms at the edges of the molecule and the π-bonds in the middle. These sorts of bonds haven’t been found in planetary materials before and the surprise is that this bond is strong and may be as strong as when hydrogen bonds to oxygen at earth temperatures."
The benzene molecules form a framework that surrounds ethane molecules in a highly symmetric geometry. The benzene molecules actually form a framework with a channel, and the ethane molecules occupy this channel.
The research on the co-crystal will continue later this year when Maynard-Casely and colleagues from the Jet Propulsion Laboratory will deuterate the co-crystal and use neutron powder diffraction for further analysis.This article is a short extract reprinted from a press release published by the Australian Nuclear Science and Technology Organisation
The detector group at the Swiss Light Source at PSI has been one of the pioneers in the development of custom-made hybrid pixel array detectors (HPADs) for synchrotron applications. In a paper published recently [Jungmann-Smith et al. (2016). J. Synchrotron Rad. 23, 385-394; doi:10.1107/S1600577515023541], this group shows that it is now possible to develop HPADs with sufficient low noise to allow single-photon detection below 1 keV as well as to perform spectroscopic imaging. A commentary has also been written about the work [Graafsma (2016). J. Synchrotron Rad. 23, 383-384; doi:10.1107/S1600577516002721].
For decades, detectors have been a limiting factor in experiments at synchrotron radiation facilities. Even though imaging detectors evolved over time, the evolution of the source always outran the evolution of the detector. This situation started to change with the introduction of the so-called hybrid pixel array detectors, which contain a pixelated readout chip custom-designed for a well-defined experiment or technique. One of the revolutionising advantages offered by this technology is that every single pixel contains all necessary electronics, including for instance counters, for X-ray detection. This massive parallelisation increased the overall efficiency of the detector by several orders of magnitude as compared with the charge-coupled-device-based system. There are now various examples of HPADs, specifically developed for X-ray experiments at storage-ring synchrotron sources, as well as various spin-off companies commercialising them. Most of these systems are so-called photon-counting detectors, where each incoming photon is processed by the readout electronics in the pixel and individually counted. The advantage of photon counting is that electronic noise, present in any system, can be efficiently discriminated against, yielding `noise-free’ detectors. An application for such low-noise systems is in energy-dispersive measurements. The researchers show in their paper that, with the use of a proper mask to shield the edge regions between pixels, very good fluorescence spectra can be obtained. This capability was subsequently used for multi-colour imaging at the SOLEIL synchrotron.
The innovative aspect of the work contained in this paper does not lie in the spectroscopic results obtained as they could very well have been obtained with other detectors. But what is truly impressive is that these results were obtained with an HPAD using a standard planar diode array as sensor. This means that the system uses relatively standard and thus easy-to-manufacture components, making it possible to envision building larger and/or further-optimised systems in the near future. And with that, low-noise HPADs have entered a field formally reserved for silicon drift detectors and complementary metal-oxide semiconductor imagers.
X-ray crystallographic analysis is one of the only methods that provides direct information on molecular structures at the atomic level. The method, however, has the intrinsic limitation that the target molecules must be crystalline, and high-quality single crystals must be prepared before measurement. These limitations have often caused considerable problems for scientists in their determination of molecular structures. In 2013, a group of scientists reported a revolutionary new technique for single-crystal X-ray diffraction analysis that did not require the crystallisation of samples in the sample preparation [Inokuma et al. (2013), Nature, 495, 461-466]. This method, later coined the crystalline sponge method, uses crystals of porous metal complexes capable of absorbing guest compounds from solution in a common solvent. The guests are efficiently trapped and concentrated at several binding sites in the porous complexes, and the periodic array of the binding sites renders the absorbed guests oriented and observable by common X-ray diffraction studies.
However, the subsequent data quality of the trapped guest compound was not very high and the use of restraints and constraints based on chemical information was necessary to refine the guest structures. The need for this workaround was due purely to unoptimised experimental conditions and protocols. It soon became clear that to develop the crystalline sponge method from basic science into a reliable new technology that might innovate and support the molecular chemistry community, considerable effort was needed to improve the data quality. In addition, the crystallographic scope and limitations in the refinement of structures with large pores — more commonly known as metal–organic framework (MOF) structures — needed to be considered carefully. Over the last two years, therefore, the same group of researchers has made considerable advances in improving the data quality and uncovering the crystallographic scope and limitations for the refinement of guest structures obtained using the crystalline sponge method [Hoshino et al. (2016), IUCrJ, 3, 139-151; doi:10.1107/S2052252515024379].
These researchers anticipate renewed interest in the technique and hope further experimentation by the community will improve the quality and value of the protocol.