# Partial orientation retrieval of proteins from X-ray free-electron-laser induced explosions for single particle imaging

## TL;DR

This paper introduces a new method to determine the orientation of proteins during X-ray imaging by analyzing how they break apart.

## Contribution

A novel approach to partially retrieve protein orientation using Coulomb explosion data from X-ray pulses.

## Key findings

- Partial orientation information can be extracted from ion ejection patterns in Coulomb explosions.
- Larger proteins show more reliable orientation retrieval using this method.
- Ion data complements traditional diffraction-based orientation algorithms.

## Abstract

Single Particle Imaging techniques at X-ray lasers have made significant strides, yet the challenge of determining the orientation of freely rotating molecules during delivery remains. In this study, we propose a novel approach to partially retrieve the relative orientation of proteins exposed to ultrafast X-ray pulses by analyzing the fragmentation patterns resulting from Coulomb explosions. We simulate these explosions for 85 proteins in the size range 100 – 4000 atoms using a hybrid Monte Carlo/Molecular Dynamics approach and capture the resulting ion ejection patterns on two virtual detectors. We exploit information from the explosion to infer orientations of proteins at the time of X-ray exposure. Our results demonstrate that partial orientation information can be extracted, particularly for larger proteins. We conclude that knowledge on ion data from X-ray laser induced explosions can directly provide the sample’s relative orientation, complementary to traditional orientation-retrieval algorithms based on diffraction patterns.