CHEMICAL CRYSTALLOGRAPHY APPLICATIONS WITH THE STOE IPDS 2T DIFFRACTOMETER EQUIPPED WITH A XENOCS GENIX CU KΑ MICROBEAM DELIVERY SYSTEM
Although Mo Kα radiation is widely used in routine small molecule structure determination, a number of applications in chemical crystallography are best treated with Cu Kα radiation. These include studies on weakly diffracting and/or very small crystals, measurements on partially disordered or fibrous samples, absolute structure determination and others. To evaluate the suitability of the STOE image-plate system IPDS2T equipped with a GeniX Cu Kα microbeam system manufactured by XENOCS for applications in chemical crystallography, trial measurements on two samples that are commonly used for testing purposes have been performed.
HIGH-THROUGHPUT SULPHUR-SAD PHASING ON A STOE IPDS 2T DIFFRACTOMETER
Chemical crystallography applications with the STOE IPDS 2T diffractometer equipped with a Xenocs GeniX Cu Kαmicrobeam system.
Solving protein crystal structures by single-wavelength anomalous diffraction (SAD) from sulphur atoms has become a widely advocated technique in recent years. This method has several appealing features, on the other hand, given that the anomalous scattering strength from sulphur atoms is rather weak at these wavelengths (f”=0.557 at Cu Kα), the data have to be collected with a very high degree of accuracy, completeness and redundancy. Such measurements are therefore ideal to test the capabilities and performances of a laboratory diffractometer setup.
POWDER EXPOSURES ON THE STOE IPDS II AND IPDS 2T-THROUGHPUT SULPHUR-SAD PHASING ON A STOE IPDS 2T DIFFRACTOMETER
On an STOE IPDS II and IPDS 2T resp. powder samples can be examined as well as single crystals. Additional accessories are not required. Textures and grain size effects can be recognized easily. Diagrams ‘intensity as a function of 2Θ’ can be created from the frames with the aid of a STOE tool.
The powder samples to be examined are filled into glass or quartz capillaries which usually have a diameter between 0.2 and 0.7 mm. During an exposure a capillary can be rotated automatically about one or two goniometer axes all the time to yield best-possible statistics. Debye-Scherrer rings (powder rings) are obtained as shown in the following example (0.5 mm capillary with silicon powder, IPDS II, 2 kW, Mo-Kα (point focus), planar graphite monochromator, 40 mm detector distance, 5 min irradiation).
