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Maximizing Data Collection Efficiency at Synchrotrons for Crystallographic Experiments

This resource delves into the nuances of collecting macromolecular crystallographic data at synchrotrons and factors to consider for optimal results. Highlights include understanding fluence, brilliance, tunability, and collimation, as well as the resources available and how synchrotron crystallography differs from lab methods. With insights on collecting data at specific endstations like SER-CAT, SBC-CAT, GM/CA-CAT, NE-CAT, LS-CAT, and BioCARS, this guide offers valuable information for researchers aiming to streamline and enhance their crystallographic experiments.

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Maximizing Data Collection Efficiency at Synchrotrons for Crystallographic Experiments

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  1. Collecting Macromolecular Crystallographic Data at Synchrotrons Andrew HowardACA Summer School, 12 July 2007 Updated slightly November 2018

  2. Synchrotrons are useful, not just fashionable • You can do almost any experiment better and faster at a storage ring than in a conventional lab; and there are experiments that you can only do at a storage ring.

  3. What we need to think about • Why synchrotrons help: Factors, parameters • How they make things harder • How synchrotron data collection is different from domestic data collection • How macromolecular crystallography is different from other storage-ring apps

  4. Fluence Brilliance Tunability Collimation Resources 1013 Xph/s/mm2 1017 Xph/s/mm2/mrad2 E = 12398.0 ± 0.4eV FWHM(v) < 100 µm Lasers, experts, labs … How synchrotrons help

  5. Some definitions and units Quantity Definition Units Value Flux # photons / Xph/ 1012 unit time sec Fluence flux / unit area (Xph/sec)/ 1013 mm2 Brilliance fluence/ Xph/sec/ 1017 solid angle* (mm2-mrad2) Brightness flux/solid angle* Xph/sec/ 1016 mrad2 * Sometimes defined in terms of bandwidth, e.g.brilliance = (fluence/solid angle)/bandwidth

  6. Which parameters really matter? • For most macromolecular crystallographic experiments fluence is the relevant parameter: we want lots of photons entrained upon a small area • Brilliance matters with very large unit cells where a high divergence is bad

  7. What does high fluence do? • Allows us to get good signal-to-noise from small samples • Allows us to irradiate segments of larger samples to counteract decay • Many experiments per day • Allows us to contemplate experiments we would never consider with lower fluence

  8. What does high brilliance do? • How do we separate spotsif the unit cell length > 500 Å? • Back up the detector • Use tiny beams • Large beam divergence will prevent either of those tools from working

  9. Tunability • Monochromatic experiments:We’re allowed to choose the energy that works best for our experiment • Optimized-anomalous experiments:We can collect F(h,k,l) and F(-h,-k,-l) at the energy where they’re most different • Multiwavelength:pick 3-4 energies based on XAS scan and collect diffraction data at all of them

  10. What energies are available? • Depends on the storage ring • Undulators at big 3rd-generation sources:3-80 KeV • Protein experiments mostly 5-25 KeV • Below 5: absorption by sample & medium • Above 25: Edges are ugly, pattern too crowded • Some beamlines still monochromatic

  11. Energy resolution &spectral width • Energy resolution: how selective we can reproducibly produce a given energy • Typically ~ 0.4 eV at 3rd-Gen sources • Need: dE < [Epeak - Eedge (Se)] ~ 1.4 eV • Spectral width: how wide the energy output is with the monochromator set to a particular value

  12. Collimation • Everyone collimates. What’s special? • Beam inherently undivergent • Facility set up to spend serious money making collimation work right • Result: we can match the beam size to the crystal or to a desired segment of it

  13. Resources Storage rings are large facilities with a number of resources in the vicinity • Specialized scientific equipment (lasers) • Smart, innovative people • Sometimes: well-equipped local labs where you can do specialized sample preparations

  14. Why wouldn’t we do this? • Beamtime might still be scarce • You’re away from your home resources • Disruption of human schedules • Travel • 24-hour to 48-hour nonstop efforts • Bad or expensive food • Extra paperwork:Safety, facility security, statistics

  15. How does synchrotron crystallography differ from lab crystallography? • Time scale very foreshortened • Multiwavelength means new experimental regimes • Distinct need for planning and prioritizing experiments • Robotics: taking hold faster @ beamlines

  16. How does macromolecular crystallography differ from other beamline activities? • “Physics and chemistry groups at the beamline do experiments; crystallographers do data collection” • Expectation: zero or minimal down-time between users • Often: well-integrated process from sample mounting through structure determination • Typical experimental times short:10 min/sample, 4 hours / project

  17. Where might we collect data? • SER-CAT: 22-ID and 22-BM • SBC-CAT: 19-BM and 19-ID • GM/CA-CAT: 23-ID multiple endstations • NE-CAT: 24-ID, multiple endstations • LS-CAT: 21-ID, multiple endstations • BioCARS: 14-BM, 14-ID

  18. Southeast Regional CAT (22) • Established ~2002 • Run as an academic consortium of about 25 universities, mostly in the southeast, with some legislative or provost-level support • 30% of my salary from there until 2014

  19. GM/CA-CAT (23) • Established around 2004 as a site for NIH GM and Cancer grantees, particularly those working on structural genomics and cancer therapeutics • First APS facility to build out multiple endstations on an insertion device line that are capable of simultaneous use

  20. BioCARS • Established around 1997 to do cutting-edge crystallographic projects, particularly involving time-resolved techniques and BSL-2 or BSL-3 samples

  21. SBC-CAT • Oldest macromolecular crystallography facility at the APS • 19-ID: more structures solved than any other beamline in the world • Good for all sizes and resolutions

  22. LS-CAT • Small consortium of academic labs • Initially funded partly by Michigan government • Built & maintained by Northwestern U • Several endstations:One tunable, the others not • Ample beamtime available

  23. Is travel necessary? • Generally not. Most beamlines have either mail-in or robotic remote access. • Mail-in: user ships samples, local staff collects data • Remote: user ships samples, staff puts puck in robotic Dewar, remote user controls experiment via network • At SER-CAT, over 90% of all data are collected either remotely or via mail-in

  24. Remote & Mail-in Realities • Advantages: • Cheaper • Schedule more flexible • Quicker change-over between users • Less safety-related paperwork • Disadvantages: • At mercy of local staff’s skill • Lose some training opportunities • Less control over experimental details • Remote: requires stable network connection

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