|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.|
Researchers in France have hit on a novel method to help kidney stone sufferers ensure they receive the correct and most effective treatment possible.
Kidney stones represent a major medical problem in the western and developing world. If left untreated, apart from being particularly painful, they can lead to renal failure and other complications. In many patients treated successfully, stone recurrence is also amajor problem. Clearly a more effective pathological approach to diagnosis and treatment needs to be identified to ensure successful eradication of stones.
Worldwide approximately 1:7000 births are affected by cystinuria, the most frequent cause of stone formation among genetic diseases. Whilst stones are treatable many therapies exist with varying results depending on the type of stone and severity of the incidence.
Cystine stones, of which there are two forms, are composed of tiny micrometre-size crystallites, which are made up of a collection of nanocrystals. Both forms of cystine stone behave in a particular way under different chemical conditions induced by the drug or drugs administered.
By crystallographic techniques Dominique Bazin, Director of Research at Université Paris-Sud 11, France (now at LCMCP-College de France), and co-workers [J. Appl. Cryst. (2014). 47, 719-725; doi:10.1107/S1600576714004658] were able to understand how some of the methods employed to medically treat the stones have different effects on the stone, from reducing the size of both nanocrystals and crystallites to changing the shape and space occupied by the crystallites at the macroscale.
Clear evidence is now available to help doctors diagnose and prescribe the correct drugs for patients with kidney stones more successfully. Trials did indicate, however, that a lot of the success that can be seen in recovery rates and non-recurrence does depend on the patient also complying with the drug regime prescribed.Jonathan Agbenyega,
Symmetry is ubiquitous in the natural world. It occurs in gemstones and snowflakes and even in biology, an area typically associated with complexity and diversity. There are striking examples: the shapes of virus particles, such as those causing the common cold, are highly symmetrical and look like tiny footballs.
A research programme led by Reidun Twarock at the University of York, UK has developed new mathematical tools to better understand the implications of this high degree of symmetry in these systems. The group pioneered a mathematical theory that reveals unprecedented insights into how different components of a virus, the protein container encapsulating the viral genome and the packaged genome within, mutually constrain each other's structures [Acta Cryst. (2013). A69, 140–150; doi:10.1107/S0108767312047150].
A paper recently published in Acta Crystallographica Section A: Foundations and Advances [Acta Cryst. (2014). A70, 162–167; doi: 10.1107/S2053273313034220] in collaboration with Pierre-Philippe Dechant from the University of Durham, UK shows that these mathematical tools apply more widely in the natural world and interestingly also account for the structures of Russian-doll-like arrangements of carbon cages known as carbon onions. It was known previously that individual shells could be modeled using symmetry techniques, but the fact that the entire structure is collectively constrained by a single symmetry principle is a surprising new result.
Such insights are crucial for understanding how different components contribute collectively to function. In the case of viruses this work has resulted in a new understanding of the interplay of the viral genome and protein capsid in virus formation, which in turn has opened up novel opportunities for anti-viral intervention that are actively being explored. Similarly, we expect that the work on carbon onions will provide a basis for a better understanding of the structural constraints on their overall organisation and formation, which in the future can be exploited in nanotechnology applications.P.-P. Dechant and R. Twarock
The development of solar panel materials that are both non-toxic and made from readily available elements rather than rare and precious metals is a priority in developing a sustainable technology. Sulfide materials containing the relatively common metals copper, tin and zinc, so-called kesterites, have been proposed as solar cell absorber materials because they comply with these two demands. Experimental solar cells using Cu2ZnSnS4 (CZTS) have demonstrated energy conversion efficiencies of 8.4% and 12% for a seleno-sulfide analogue. New structural information is crucial to improving on these figures still further.
Unfortunately, kesterites are not amenable to conventional X-ray diffraction because copper and zinc ions are indistinguishable. Now, Alain Lafond and his colleagues at Nantes University and Pierre Fertey from Soleil synchrotron have demonstrated that it is possible to carry out resonant diffraction of a single crystal of the semiconductor CZTS.
The powdered precursor was prepared using a ceramic synthesis at a high temperature (1023 K) from the corresponding elements Cu, Zn, Sn and S. The product is heated for a further 96 hours to anneal it before it is plunged into ice-water to lock in the chemical structure present at that elevated temperature, a process known as quenching. Tiny single crystals of sufficient quality for X-ray diffraction were picked out of the powder. The researchers used laboratory powder X-ray diffraction and energy-dispersive X-ray spectroscopy analyses to test the purity of their product. They then carried out high-performance resonant diffraction on the CRISTAL beamline at the Soleil French synchrotron, which gives them the possibility to adjust the radiation wavelength in order to enhance the contrast between copper and zinc.
The data they obtained showed the annealing process generates a disordered structure that can be distinguished from the order kesterite structure despite the otherwise similar X-ray scattering pattern that would be generated by the copper and zinc ions in the ordered form. The team points out that the fabrication process for making a thin absorber film from CZTS in a solar panel is carried out at an elevated temperature and the disordered form is likely to be the active form produced which probably precludes high photovoltaic performance.
The findings offer important clues for the development of CZTS and related materials that avoid expensive and rare materials such as indium and tellurium in solar cells.
"The next step in this research is to determine the relationship between the synthesis conditions (quenching or slow cooling) and the actual Cu/Zn distribution in the kesterite structure," Lafond told us. He revealed that a new proposal to the Soleil French Synchrotron Facility has been deposited for the next experimental period and in the meantime structural disorder in kesterite materials can be investigated by solid-state NMR and Raman spectroscopy.
Researchers in China [J. Appl. Cryst. (2014). 47, 527–531; DOI: 10.1107/S1600576713034535] have found a convenient way to selectively prepare germanium sulfide nanostructures, including nanosheets and nanowires, that are more active than their bulk counterparts and could open the way to lower cost and safer optoelectronics, solar energy conversion and faster computer circuitry.
Germanium monosulfide, GeS, is emerging as one of the most important "IV–VI" semiconductor materials with potential in opto-electronics applications for telecommunications and computing, and as an absorber of light for use in solar energy conversion. One important property is its much lower toxicity and environmental impact when compared with other semiconductors made with cadmium, lead and mercury. It is less costly than other materials made with rare and noble metal elements. Indeed, glassy GeS has been used in lasers, fibre optic devices and infrared lenses as well as rewritable optical discs and non-volatile memory devices for several years. It is also used extensively as a solid electrolyte in conductive bridging random access memory (RAM) devices.
The repertoire of this material might be extended much further with the extra control that its use as nanostructured systems might allow. Liang Shi and Yumei Dai of the University of Science and Technology of China, in Hefei, point out that research in this area has lagged behind that with other IV–VI semiconductors. They hope to change that and have focused on how nanosheets and nanowires of GeS might be readily formed. They have used X-ray powder diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry and scanning electron microscopy to investigate the structure, morphology, composition and optical absorption properties of their samples.
The team used simple "wet" chemistry to synthesize their products using germanium dichloride–dioxane complex, thiourea and oleylamine (OLA) as starting materials. The ingredients were mixed in a sealed reaction flask, blasted with ultrasound to exclude air and then stirred and heated. The team was able to make nanosheets of GeS this way if the process was carried out for several hours at 593 K. At higher temperature, 613 K, they found that the sheets wind up into nanowires. Indeed, the precise heating time and temperature allowed them to control the structure of the final product. The team suggests that the rolling up of the nanosheets into nanowires is driven by the surface tension between the sheet and the OLA molecules during the heating.
Having proven the structural integrity of their GeS nanowires and nanosheets, the team built several test devices – a photoresponsive unit – which they used to evaluate the optical and electronic properties of the products. The team says that they have demonstrated "outstanding photoresponsive behaviour". This "indicates the potential use of as-synthesized GeS nanosheets and nanowires in solar energy conversion systems, such as the fabrication of photovoltaic devices".
Business development manager, IUCr