UV-visible Microspectroscopy at the instrument BIODIFF

Topic  38
Main supervisor T.Schrader (t.schrader@fz-juelich.de)
MLZ institution FZJ
Local supervisor 1 Christian Göb
Institution Rigaku Europe SE
Local supervisor 2
Local supervisor 3
Local supervisor 4
Title UV-visible Microspectroscopy at the instrument BIODIFF
Description Single crystal neutron diffraction experiments on protein crystals often require beamtimes of several days in order to measure a complete data set which leads to meaningful results on atom positions and occupancies. In case of room temperature measurements, the sample under investigation might change during that time. For example, if one wants to study a radical intermediate state of a protein, which is often linked to a distinct UV-visible absorption maximum of the crystal, one is often interested in the decay of the number of radicals in the crystal. Below a certain number, one would rather switch to another freshly prepared crystal. This would save precious neutron beamtime.
At synchrotron beamlines, UV-Visible microspectroscopy of the crystals mounted on the goniometer is readily available. The purpose of this set-up is to measure the UV-visible spectrum of an oriented crystal on the beamline. This has the advantage that the crystal orientation relative to the light beam and polarization is known. Thereby, the absorption dipole moment of a protein ligand or the radical state can be specifically addressed with polarized light.
At neutron instruments, such microspectroscopy set-ups are usually not found. In this GNEUS project, we develop such a set-up for the instrument BIODIFF borrowing from the experience of our colleagues at x-ray beamlines. In parallel and independent on any reactor operation schedule, one can test this set-up at our Rigaku home source x-ray diffractometer with our industrial collaborator Rigaku. As a first relevant organic crystal sample, one can investigate the 2p-2p photoaddition of a cinnamic acid compound which is a yet not fully understood single crystal to single crystal transition. But the candidate is free to suggest own systems and proteins/ligands as for example proteins digesting the microplastic found in the oceans. Time permitting, this project could extend the spectroscopy into the near IR or even mid-IR range where the crystals show distinctive (overtone) vibrational bands linked to its ligand or its radical state.