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- 4th International SAXS/GISAXS Workshop (PDF)
Sep 09-11, Leoben, Austria - Navigated Atomic Force Microscopy - N8 NEOS
Sep 15, Free Webinar - 17th Bruker Users‘ Group Meetings 2010 - Single Crystal X-ray Diffraction
Sep 19-22, Karlsruhe, Germany - Good Diffraction Practice III - Powder XRD Instrumentation and Data Quality
Sep 30, Free Webinar - COM2010 - Conference of Metallurgists
Oct 03-06, Vancouver, British Columbia, Canada
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IμS with Copper Radiation - Absolute configuration from light atom structures
The IμS with Quazar optics delivers a 2D focused beam with an unprecedented flux of more than 5 x 109 X-rays/(s mm2). The excellent beam stability guarantees high data quality allowing absolute structure determination on very small samples with no atoms heavier than oxygen.
- Vitamin C
Absolute configuration of Vitamin C
Intensity data were collected on a small crystal of Vitamin C (40 μm x 100 μm x 100 μm) using an APEX II QUAZAR with Cu radiation. Data are 10 fold redundant and complete to 0.83 Å. The structure refines with a reliability criteria R1 of 2.25% a Flack x parameter of 0.03(15) and an Hooft y parameter of 0.04(16).
The determination of absolute configuration
Currently, the established method to determine the absolute configuration of a chiral molecule calls for the determination of the Flack x parameter. Flack, H.D. (1983). Acta Cryst. A39, 876-881. A new statistical method based on Bayesian statistics was developed by Rob Hooft et al. J. Appl. Cryst. (2008). 41, 96-103 and determines the Hooft y parameter.
It is possible to determine the absolute structure of chiral compounds by accurately measuring the small differences (Bijvoet anomalies) of Friedel pairs. Data have to be collected very carefully using highly performing instrumentation to allow the detection of these small differences in measured intensity data.