The goal of this research is to obtain a fundamental understanding of the non-adiabatic processes that occur during irradiation of radiosensitisers by ion and light sources. In particular, ionization and fragmentation of these molecules will be studied in the gas phase and in the presence of water. The overarching goal is to understand how the presence of an environment modifies the response and to obtain detailed information on the charged products that are produced.
We will study irradiation processes in two exemplar systems, namely nucleobases and 5-halouracils. The 5-halouracils are radiosensitisers that are widely used in cancer treatments. They are formed when a halogen atom, such as fluorine (5-FU) or bromine (5-BrU), replaces the C5 hydrogen in uracil and can be used to replace thymine in DNA. When exposed to radiation such as ions or photons, lethal damage to DNA containing these radiosensitisers is magnified and so they find therapeutic use in destroying cancerous cells. Ionization was found to increase mispairing of 5-FU and 5-BrU with guanine . This mispairing is due to isomerization of the 5-halouracil to its enol form and so nuclear dynamics initiated by electronic processes is crucial to the mispairing process.
To date, a lot of research on non-adiabatic dynamics in uracil and 5-halouracils has focussed on fragmentation processes [2, 3, 4]. For instance, by studying the fragmentation products of 5-FU by high-frequency radiation pulses the electronic processes leading to the formation of particular ions was extracted . Additionally, photoelectron spectra (PES) for uracil have been calculated using the multi-configurational time-dependent Hartree (MCTDH) method and the molecular dynamics of its radical cation studied . However, all these studies have been in the gas phase. Understanding how dynamical processes in these molecules are altered by the presence of water is essential for realistic modelling of biological systems. To date, pioneering simulations of the interaction of low energy electrons with DNA bases in the presence of liquid water and amino acids have been carried out [5, 6, 7, 8]. However, these simulations have considered an adiabatic treatment of the dynamics.
In this project we will mainly use non-adiabatic quantum molecular dynamic (NA-QMD) methods, developed by Dr Dundas in QUB and Prof. Suraud in Toulouse, for studying fragmentation processes induced by irradiation. At the heart of the NA-QMD approach is a time-dependent density functional theory (TDDFT) treatment of the electronic dynamics together with a classical description of the nuclear dynamics. This approach is implemented in a parallel code called EDAMAME (Ehrenfest DynAMics on Adaptive MEshes) . This code has been recently used to study ionization processes in benzene and acetylene [10, 11, 12]. In addition, there will be an opportunity to use another state-of-the-art NA-QMD code (PW-TELEMAN) developed by Prof. Suraud and co-workers .
The following aspects will be considered.
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