DEVELOPMENTS FOR SINGLE CRYSTAL XAS INSTRUMENTATION

Stanford University, Stanford CA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Single crystal x-ray absorption spectroscopy allows for the sequential measurement of x-ray diffraction and x-ray absorption data enabling the experimenter to obtain simultaneous global structure and atomic-level local structure information of a protein or small molecule active site. Incremental changes were made to the single crystal XAS setup during 2009. A mechanical rearrangement enabled the Mar345 image plate detector (which is larger than the original Mar165 CCD) to be more optimally positioned for improved centering with respect to the beam and accordingly a higher accuracy in the determination of crystal orientation matrices and cell parameters. The sensitivity of the liq He cryostream was tested on protein samples that are especially susceptible to binding and reactivity with dioxygen. These tests will be extended to samples that have been irradiated with x-rays to investigate changed rates of oxygenation with possible photo-excitation of the molecule and changes in redox potentials.