BL12-2

BL12-2 is optimized for high-throughput micro-crystal macromolecular crystallography data collection to high-resolution.  BL12-2 also supports advanced serial and time-resolved crystallography methods.  BL12-2 is an undulator beam line with a fully adjustable focus. Micron-sized beams (10 x 10 µm2 or 20 x 20 µm2) are achieved with precision micro-collimators. BL12-2 is SAD and MAD capable and can be run in a fully remote access mode. 

BL12-2’s X-ray source is a 134-pole, 1-Tesla in-vacuum undulator. The beamline optics include a flat side-deflecting Rh-coated Si mirror and a liquid nitrogen-cooled double-crystal Si(111) monochromator with a 0.013% energy bandpass producing ~4x1012 p/s at the Se edge with a usable energy range of 6.7-17 KeV. Kirkpatrick-Baez (KB) optical mirrors are used for horizontal and vertical beam focusing yielding a vertical beam focus of 15 µm FWHM.  BL12-2 is equipped with an Eiger2 XE 16M pixel array detector with a readout speed of up to 500 Hz which enables ultra-high-redundancy SAD experiments and high-speed micro-crystal x-ray rastering to locate and optimally expose small crystals.

Features and Techniques

Bright X-ray Microbeams – X-ray Microbeams (10-50 µm) can be used to study very small microcrystals and in some cases, they can be used to select portions of larger crystals with improved diffraction of up to 0.5 Å resolution. 

Remote Access - Users control and carry out their experiments and run processing software in real time from anywhere in the world. This is accomplished with a simple free app that runs on the user's remote computer which connects to a server running at SSRL.

Large Unit Cells - Diffraction from very large unit cells (for example, viruses and large complexes) can be resolved with pixel array detectors (PADs). They have large detection areas and can be placed long distances from the sample, and they have excellent intrinsic resolving power and no pixel crosstalk.
Automated Screening - Samples are systematically mounted from a frozen cassette or an ambient temperature container using a robot and subsequently aligned, exposed, indexed, and assigned a score for overall diffraction quality.

High Speed X-ray Rastering - Low-dose X-rays are used to accurately locate microcrystals or other visually obscured crystals in loops and other mounts, or to identify areas of a crystal that have improved diffraction. A typical 400 µm diameter Mitogen Mesh can be fully scanned in 2 minutes using a beam and step size of only 10 µm.

Serial Fixed-Target - Multiple crystals are mounted in predetermined locations on a grid so that diffraction data can be collected from each crystal in rapid succession. SSRL grids or user-supplied high-density crystal mounts can be used.  X-ray rastering or AI-based video analysis tools can rapidly identify and position small crystals.

MAD/SAD Phasing - Multi- and single wavelength anomalous diffraction (MAD and SAD, respectively) is used to solve the phase problem in structure determination.  Accurate heavy atom absorption edge spectra provide the most useful energies (f' and f") for MAD data collection.  High-speed ultra-redundant data collection can be used to obtain significant signal from weak anomalous scattering atoms such as sulfur.

Metal Identification – Excitation scans are useful to quickly determine the heavy element content in crystals.  The excitation scan measures the fluorescence counts from any element present in the sample with an absorption edge below the excitation energy. Excitation scans take less time than the MAD scans and thus are a faster way to determine the presence of a heavy atom derivative/ligand in the sample.

Source - 134-pole, 1-Tesla in-vacuum undulator.

For more information on the features of BL9-1, see the Macromolecular Crystallography Website: https://smb.slac.stanford.edu/