NEW FLOW CELLS FOR HIGHER-THROUGHPUT SOLUTION SCATTERING STUDIES

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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. We have recently developed two types of flow cells to improve data collection efficiency in solution x-ray scattering studies of biological macromolecules. Both cells incorporate a thin-wall quartz or borosilicate glass capillary of 1.5 mm nominal diameter to hold a sample aliquot as little as ~5 microliter in the x-ray beam. The first type has the capillary positioned at the center of a short cylindrical aluminum piece which has a NW25 vacuum fitting on both ends. It is directly connected to the window flange immediately downstream of the sample stage and the other end is connected to the guard slit, immediately upstream of the sample stage, via a short flexible below. It has achieved an absolutely minimum background level, which is required for studying small proteins and peptides, by eliminating the air gap completely by connecting together the upstream and downstream vacuum paths. The second flow cell complements the first one by having the capillary outside of the vacuum path for much quicker alignment, allowing users to switch from the standard polycarbonate cells within a very short time upon encountering severe radiation damage which can be effectively eliminated in most cases by flowing the sample aliquot gently in the beam. A mere 7 mm air gap is required for this cell, and the background level is still reasonably low for most solution scattering studies. This design also allows easier troubleshooting than for the in-vacuum version. Either cell is connected to a Hamilton 540B sample dispenser via thin Tygon tubing for sample loading and flow remotely controlled by Blu-ICE. In both cases, sample temperature control is accomplished via flowing water through the cell body using a standard refrigerated Neslab water bath.