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Electron-collision induced fragmentation and intermolecular energy transfer processes in water and hydrated biomolecule clusters studied with multi-particle coincidence experiments

Subject Area Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Term from 2016 to 2020
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 328557844
 
Final Report Year 2020

Final Report Abstract

In this project, we demonstrated a damage mechanism of biochemically relevant systems in the form of a non-local autoionizing process called intermolecular Coulombic decay (ICD). It directly involves DNA constituents or organic molecules in an aqueous environment. The products are two energetic ions and three reactive secondary electrons that can cause further damage in their vicinity. Hydrogen-bonded complexes that consist of one tetrahydrofuran (THF) moleculea surrogate of deoxyribose in the DNA backboneand one water molecule are used as a model system. After electron-impact ionization of the water molecule in the inner-valence shell the vacancy is filled by an outer-valence electron. The released energy is transferred across the hydrogen bridge and leads to ionization of the neighbouring THF molecule. This intermolecular energy transfer from water to THF is faster than the otherwise occurring intermolecular proton transfer. The signature of the ICD reaction is identified in triple-coincidence measurements of both ions and one of the final state electrons. These results could improve the understanding of radiation damage in biological tissue. Moreover, by using the hydrogen-bonded pure and mixed dimers of the heterocyclic THF molecule and water, we investigated also the role of water environment in the fragmentation of biomolecules induced by low-energy (< 100 eV) electrons. For ionization of these dimers, a molecular ring-break mechanism is observed, which is absent for the THF monomer. Employing coincident fragment ion mass and electron momentum spectroscopy, and ab initio calculations, we find that ionization of the outermost THF orbital initiates significant rearrangement of the dimer structure increasing the internal energy and leading to THF ring-break. These results demonstrate that the local environment in form of hydrogen-bonded molecules can considerably affect the stability of molecular covalent bonds.

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