30th Annual SSRL Users' Meeting — October 9-10, 2003

Instrumentation for Polarized XAS of Protein and Inorganic Single Crystals at SSRL

M. J. Latimer and B. Hedman

Stanford Synchrotron Radiation Laboratory, SLAC, Stanford University, Stanford, CA 94305

Polarized XAS of specifically oriented crystals offers a wealth of molecular and electronic structure information unavailable in un-oriented/isotropic systems. By alignment of molecular vectors to the e-vector of the x-ray beam, specific electronic transitions or EXAFS interactions can be emphasized or minimized. The angle-dependence of the polarized XAS signals allow direct electronic-molecular structure correlations and the precision of XAS distance determinations provide more detailed structural information for metallo-protein active sites than can be provided by crystallography alone.

Development of single crystal XAS instrumentation, which allows nearly simultaneous XAS and crystallographic data collection, has been carried out at SSRL BL9-3, the 16-pole 2T wiggler beam line 9 side station dedicated to general user biological XAS. The implementation includes a Huber kappa goniometer, Canberra 30-element Ge detector for XAS data collection, open-flow He and N2 coolers, microscope for crystal alignment in the beam, and a MAR CCD or MAR 345 crystallography detector. The kappa goniometer allows a large accessible angle range with an open geometry affording access to detectors and open stream coolers. Applicable standard hardware on SSRL crystallography beam lines has been incorporated with crystallographic data collection controlled via the Blu-Ice software developed by the SSRL SMB macromolecular crystallography group. XAS data collection is handled through the SSRL standard XAS-Collect software. Initial diffraction and XAS data from single crystals using an open flow cryostat will be presented. The instrument will be available to general users after the SPEAR3 upgrade in early 2004.