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Acta Cryst. (2014). A70, C965
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The determination of the absolute configuration for light-atom structures is central to research in pharmaceuticals and natural-product synthesis [1]. In the absence of elements heavier than silicon, it is often problematic to make a significant assignment of absolute configuration. Traditionally, heavy-atom derivatives were prepared which have a stronger anomalous signal compared to the native compound. However, this is not always feasible. The assignment of the absolute structure of pure organic compounds has become somewhat easier with the advent of high-intensity microfocus sources [2], as the increased flux density improves the anomalous signal through improvements in counting statistics. In order to maximize the anomalous signal, X-ray sources with Cu anodes are usually used for the absolute structure determination. However, these data are usually limited to a maximum resolution of about 0.80 Å. High-brilliance microfocus X-ray sources with Mo targets enable the collection of high quality data beyond 0.40 Å within a reasonable amount of time. This allows not only a more accurate modelling of the electron density by using aspherical scattering factors, but also enables a reliable determination of the absolute structure, despite the significantly lower anomalous signal obtained with Mo Kα radiation. With the recently introduced liquid-Gallium-jet X-ray source unprecedented beam intensities can be achieved [3]. The shorter wavelength of Ga Kα compared to Cu Kα slightly weakens the anomalous signal of a typical light-atom structure. However, due to the shorter wavelength, the highest resolution for the liquid metal-jet source is typically at about 0.70 Å, compared to about 0.80 Å for Cu Kα. Hence, about 50% more unique reflections can be recorded. This clearly improves the structural model and the quality of the Flack parameter. Selected results on the absolute structure and charge density determinations for light-atom structures will be presented.

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Acta Cryst. (2014). A70, C1330
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Parasitic scattering caused by apertures is a well-known problem in X-ray analytics, which forces users and manufacturers to adapt their experimental setup to this unwanted phenomenon. Increased measurement times due to lower photon fluxes, a lower resolution caused by an enlarged beam stop, a larger beam defining pinhole-to-sample distance due to the integration of an antiscatter guard and generally a lower signal-to-noise ratio leads to a loss in data quality. In this presentation we will explain how the lately developed scatterless pinholes called SCATEX overcome the aforementioned problems. SCATEX pinholes are either made of Germanium or of Tantalum and momentarily have a minimum diameter of 30µm. Thus, these novel apertures are applicable to a wide range of different applications and X-ray energies. We will show measurements which were performed either at home-lab small angle X-ray scattering (SAXS) systems such as the NANOSTAR of Bruker AXS or at synchrotron beamlines. At the PTB four-crystal monochromator beamline at BESSY II data was collected for a comparison of conventional pinholes, scatterless Germanium slit systems and SCATEX pinholes. At the Nanofocus Endstation P03 beamline at PETRA III we compared the performance of our SCATEX apertures with conventional Tungsten slit systems under high flux density conditions.
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