Juergen Graf

Absolute configuration determination for light-atom structures using low-power microfocus X-ray source

The determination of the absolute configuration for light-atom structures has become central to research in pharmaceuticals and natural products synthesis. In the absence of elements heavier than silicon, it is often problematic to make a significant assignment of absolute configuration, especially for smaller crystals. Besides the introduction of new mathematical methods to evaluate the Bijvoet differences, the assignment of the absolute structure for light atom compounds has become easier with the advent of high-intensity microfocus sources, as the increased flux density improves the anomalous signal through improvements in counting statistics. In this presentation, we will be reviewing the current performance levels of different low power microfocus X-ray sources, such as the IμS and the METALJET X-ray source. Further, we will be discussing the main features of the newest generation of the IμS. We will be presenting selected results to demonstrate the impact of these modern microfocus X-ray sources on the data quality for applications in chemical and biological crystallography.

Multilayer optics and scatterless apertures for high-brilliance X-ray sources

Scatterless apertures, such as scatterfree pinholes, are usually made of oriented single crystals, such as Ge or Ta, and show a significant reduction of parasitic scattering commonly associated with conventional metal apertures. Therefore, such pinholes allow an improvement of X-ray analytical instruments as the number of necessary pinholes can be reduced. Further, the use of scatterfree pinholes enables a significant reduction of the background. This improves the data quality at low resolution which is beneficial for small angle scattering, as well as for crystallography applications. Our SCATEX pinholes are either made of Germanium for energies below 11.2 keV or of Tantalum for energies above 11.2 keV and are available with diameters ranging from 2 mm down to 20 μm and below. Therefore, these novel apertures are applicable to a wide range of different applications. We will be showing new results about development and use of these pinholes.

Current Status of Microfocus X-ray Sources for Chemical and Biological Crystallography

Modern microfocus X-ray sources define the state-of-the-art for most applications in X-ray diffraction. These sources are usually combined with multilayer X-ray mirrors which are excellent X-ray optical devices for beam shaping and preserving the brightness of the source. Microfocus rotating anode generators and liquid metal jet systems deliver flux densities in the range of 1011 photons/s/mm2. However, these sources are expensive and need regular and sometimes time-consuming maintenance. Low power microfocus sealed tube sources, such as the Incoatec Microfocus source IμS, represent an interesting low-maintenance alternative to rotating anode generators. Power loads of several kW/mm2 in anode spot sizes of < 50 μm deliver a small and bright beam. Flux densities of up to 1010 photons/s/mm2 can be achieved in a focused beam suitable for most protein crystals and poorly diffracting small molecule samples. The latest generation of the IμS, the IμS 3.0, is the first microfocus X-ray source that is optimized for X-ray diffraction resulting in a gain in intensity of about 30% compared to its predecessor. In this presentation, we will be reviewing the current performance levels of different microfocus X-ray sources. Further, we will be discussing the main features of the newest generation of the IμS. We will be presenting selected results to demonstrate the impact of these modern microfocus X-ray sources on the data quality for applications in chemical and biological crystallography.

Improvement of SAXS Lab Equipment by Using Scatterless Apertures

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.