Cold Beams of Large Molecules for Structural Dynamics Studies

Abstract

Biomolecules and their reactions are of great interest because they are important for the functions in our body and thus for health. The structure of a molecule defines its function, and in this work we demonstrate the crucial steps that will allow direct recording of structural information from large biological molecules through gas-phase x-ray diffraction. This requires a source of intact biomolecules in the gas-phase, as well as the ability to ensure all molecules in the x-ray focus are structurally identical. In this thesis it is shown how this can be achieved using a laser desorption molecular beam source in combination with electrostatic deflection.

Following an introduction into the subject and a brief review of the theoretical background in the first two chapters, chapter 3 contains the details of our new laser desorption source for thermally labile biomolecules, that is fully compatible with use at central facilities. Afterwards, a characterisation of the laser-desorption molecular beam source is presented in chapter 4. Utilizing strong-field ionisation, we characterised the produced molecular beam and evaluated the influence of various experimental parameters. Strong-field ionisation acted as a universal probe and enabled us to analyse the purity of the produced molecular beam, including molecular fragments. The optimised source was then combined with an electrostatic deflector for species separation. In chapter 5 it is shown that a cold molecular beam of Ac-Phe-Cys-NH2 is produced and the conformers are spatially separated. This is the first demonstration of conformer-selected and rotationally cold molecular beams of peptides, which is a crucial step towards the implementation of single-molecule diffractive imaging experiments of biological systems. Additionally, it was possible to produce a molecular beam of glycine with the laser desorption source. Combined with the electrostatic deflector one of the conformers of glycine could be separated from the other two, shown in chapter 6, enabling novel conformer-resolved ultrafast dynamics experiments. In chapter 7 the applicability of the source to even larger biomolecules, through first measurements of insulin, is demonstrated. In the last two chapters a summary and outlook is given and several improvements and follow-up experiments are suggested.