Synchrotron data collection

The major advances in crystallographic methods were both experimental and theoretical. In experimental terms, there was widespread availability of synchrotron data collection resources and the emergence of CCD detectors that dramatically increased the speed at which data could be collected. A particularly important advance was the development of cryocrystallography methods [39] that revolutionized crystallography by making crystals essentially immortal. 

TabU IV. RUF4 X tay Synchrotron Data Collection inslrumenl Brodchaven National Laboratory, National... 

Laue Method for Macromolecule X-Ray Diffraction. As indicated above it is possible to determine the stmctures of macromolecules from x-ray diffraction however, it normally takes a relatively long period of data collection time (even at synchrotrons) to collect all of the data. A new technique, the Laue method, can be used to collect all of the data in a fraction of a second. Instead of using monochromated x-rays, a wide spectmm of incident x-rays is used. In this case, all of the reflections that ate diffracted on to an area detector are recorded at just one setting of the detector and the crystal. By collecting many complete data sets over a short period of time, the Laue method can be used to foUow the reaction of an enzyme with its substrate. This technique caimot be used with conventional x-ray sources. 

Unsubstituted, unsolvated complexes have been observed for all metals, but their low solubility prevents the growth of quality single crystals. This problem was recently overcome with data collected on a powder sample on a synchrotron X-ray source followed by Rietveld refinement.17-19 Not surprisingly, the structures display polymeric chains with alternating metal and Cp units. 

Time-Resolved Crystallography. Time-resolved crystallography (TC) uses an intense synchrotron X-ray source and Laue data collection techniques to greatly reduce crystallographic exposure times. Normal time resolution for X-ray... 

A number of synchrotrons (including the National Synchrotron Light Source, New York, the Advanced Light Source, Berkley, and soon the Canadian Light Source, Saskatoon) operate mail-in crystallography services where a scientist can mail in crystals (prefrozen and mounted on loops) and data will be collected, processed (sometimes), and returned. This is becoming a method of choice, as it eliminates the need to travel to a synchrotron and speeds up the data collection procedure at the synchrotron also. 

KcsA crystals suitable for X-ray crystallographic analysis using synchrotron radiation were obtained and the data collected and analyzed for multiple crystals and six different data sets as described in the 1998 Science publication (reference 15). The final KcsA pore structure, including amino acid residues 23 to 119 of the K+ channel, refined to 3.2 A. The X-ray data were deposited in the Protein Data Bank with the accession number 1BL8. 

Rietveld refinement [25, 26] is a method of whole pattern refinement, where a calculated diffraction pattern for a structure model is a least-squares fit to an observed diffraction pattern. Originally, it was used as a means of verifying proposed structure models. For zeolites, Rietveld refinement is still used for the same purpose and provides details of the structure including atomic positions of framework atoms and cation sittings. Data with accurate intensities and well-resolved peaks are needed for the most accurate work, and so often a synchrotron source is used for data collection since it can provide higher intensity and peak resolution than an in-house diffractometer. However, modern in-house diffractometers often provide good enough data for some refinements. 

Synchrotron beam time remains a scarce resource world-wide, however wiA over 30 synchrotron raAation centers eiAer operational or under construction, most prospective users can obtain access to Ae facilities (11). In most cases, beam time is available free of charge for non-proprietary research. Access to a facAty is often by means of a peer reviewed proposal. Adequate equipment for sample handling and data collection is available at most synchrotron raAation laboratories. Many laboratories also provide software for data analysis. 

In this Chapter I have focused on in-house data collection, as data collection at synchrotrons is covered in this volume by Wasserman et ah, Chapter 12. Naturally, the techniques and strategy for collecting data in-house and at synchrotrons have a great deal in common. 

High-throughput crystallographic data collection at synchrotrons... 

Rapid collection of diffraction data depends on access to such powerful X-ray sources. This chapter describes how high-quality, high-throughput data collection can be achieved. We use SGX-CAT, the SGX Collaborative Access Team beamline, located at the Advanced Photon Source of Argonne National Laboratory as an example to illustrate the concepts behind the design of, and the hardware used at, synchrotron beamlines. Many of these features are found, individually or in combination, at other beamlines. Data collection at synchrotron sources produces enormous quantities of data. We, therefore, also discuss the information technology infrastructure and software that is necessary for effective data management. 

Crystallographers have traditionally travelled to synchrotrons for data collection. However, this approach is not generally compatible with high-throughput data collection. For example, significant time is often expended merely in transporting technical staff to the synchrotron facility. 

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