T-REXX: a new endstation for serial time-resolved crystallography

by David von Setten (EMBL)

109 (25b)



EMBL operates two beamlines (P13 and P14) for macromolecular crystallography at the PETRA-III synchrotron. A second endstation (‘P14.EH2’, ‘T-REXX’) for serial time-resolved crystallography is in operation in a second hutch at the far end of P14 since October 2018. For this endstation, the P14 X-ray beam is refocussed with a compound refractive lens (CRL) transfocator to provide a 15x10 μm2 beam with a flux of about 2e12 photons/s at 12.7 keV. To be able to accommodate different microcrystal sample delivery systems suitable for serial crystallography, T-REXX is not equipped with a goniometer, but instead with a beam shaping device (BSD) that provides an on-axis viewer, beam shaping apertures, a fully motorized beamstop, and a scintillator for visualisation of the X-ray beam. For time-resolved pump/probe experiments, a laser system (355 nm) for initiating reactions is built into the setup, such that the laser and X-ray beams are almost parallel at the sample position, which facilitates alignment of the beams using the on-axis viewer. First experiments have yielded promising results using different sample delivery systems, such as microfluidic flow cells as well as patterned silicon chips (Mehrabi et al., Nature Methods 16, 979 (2019)). In the future, the Hadamard technique (Yorke et al., Nature Methods 11, 1131 (2014)) will be employed to reach sub-millisecond timescales in time-resolved experiments, either by gating the detector or alternatively by modulating the X-ray beam.