Ramona Duman
Key Research Area
Fragment-based drug discovery.
Latest Publications
Sample preparation for in-vacuum X-ray diffraction
Introducing cryo-cooled protein crystals to the vacuum environment is a crucial step in the preparation for long-wavelength diffraction studies. For this purpose, on beamline I23, we currently use equipment designed for cryo-electron microscopy, which has been modified to accommodate protein crystals. My work focuses on optimizing the sample preparation with the aim to improve the quality of the diffraction data we collect. Two aspects in particular are under active investigation: sample mounting and removing excess liquid surrounding the crystals. The former involves searching for a material which satisfies two important criteria: low X-ray absorption and scattering and a good thermal conductance, to allow efficient cooling of the sample in vacuum. The latter aims to minimise the X-ray absorption effects caused by excess mother liquor, by removing this without perturbing the structural stability of the crystal.
X-ray tomography
The enhanced anomalous signal measurable at long-wavelengths comes at the price of increased absorption of X-rays by the irradiated samples. To address this, we are going to investigate applying analytical correction factors to all Bragg intensities.
The complex in-vacuum sample environment on I23 is equipped with a tomography camera, currently in early commissioning stage. This setup will complement diffraction experiments with X-ray imaging for the purpose of reconstructing the irradiated volume of the sample, as well as estimating the path lengths of X-rays through the crystal. One initial challenge to overcome is the low absorption contrast between the protein crystal and the surrounding non-diffracting material.
Sample delivery for serial crystallography and XFEL experiments
I am involved in a collaborative project with teams from Paul Scherrer Institut, Switzerland, and DESY, Hamburg, aimed at developing sample delivery for serial crystallography and XFEL experiments using a Si-chip fixed target. This has been successfully used to collect room-temperature and cryo modes and is actively being developed to include other challenging sample setups.
