DEVELOPMENTS FOR SINGLE CRYSTAL XAS INSTRUMENTATION

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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. The single crystal experimental setup has been improved through the installation of a second pair of x-ray slits for precise beam definition. A beam collimator has also been installed to minimize beam scatter. Test experiments show that these additions greatly decrease background signal arising from the crystal mount. Exploratory experiments on crystals in low oxidation states have been carried out, which indicate that a liquid helium cryo-cooling device is insufficient in maintaining an anaerobic atmosphere around the crystal, leading to slow crystal oxidation. A liquid nitrogen cooling protocol is being developed to address this issue and will be tested in the next few months.