MS23-P12 Experimental and computational reduction of dynamical electron scattering allows visualizing individual hydrogen atoms Max Clabbers (C-CINA, Biozentrum, University of Basel, Basel, Switzerland) Tim Gruene (Paul Scherrer Institut (PSI), Villigen, Switzerland) Eric van Genderen (Paul Scherrer Institut (PSI), Villigen, Switzerland) Jan Pieter Abrahams (Paul Scherrer Institut (PSI), Villigen, Switzerland)email: clabbersm@gmail.comElectron crystallography allows structure solution of beam-sensitive organic pharmaceuticals and macromolecules when only nanometre-sized crystals are available. Compared to X-rays, electron diffraction faces a crucial challenge: dynamical electron scattering compromises structure solution and its effects can only be modelled in specific cases. Dynamical scattering can be reduced experimentally by decreasing crystal size – but not without a penalty, as it also reduces the overall diffracting intensity. To boost the very weak diffraction data, the crystals were cryo-cooled and we employed a fast and highly sensitive hybrid pixel detector. Here we show that nanometre-sized crystals from organic pharmaceuticals allow visualization and unconstrained positional refinement of the hydrogen atoms, even whilst ignoring the effects of dynamical scattering during refinement. Furthermore, we introduce a general likelihood-based computational approach for further reducing the adverse effects of dynamic scattering, which significantly improved model accuracy – even for protein crystal data at substantially lower resolution.

Keywords: electron diffraction, hydrogen atoms, dynamical scattering