Ultraviolet liquid-microjet photoelectron spectroscopy of aqueous solutions

Liquid-microjet photoelectron spectroscopy provides a direct way of measuring valence electronic structure; however, its application to solutions had been hampered by a lack of detailed understanding of the experimental parameters and procedures, and the impact of inelastic scattering of low energy electrons. A major part of the work described in this thesis is the development of rigorous experimental procedures to ensure accurate and reproducible UV photoelectron spectra of liquids, described in Chapter 2. These experimental procedures were then applied to record accurate UV photoelectron spectra of liquid water, and aqueous solutions of phenol, a common biological motif, and thymine, a DNA base. These studies aimed to elucidate the electronic structure of the liquid water (Chapter 3), aqueous phenol (Chapter 4) and aqueous thymine (Chapter 5) and how indirect ionisation processes affected their ionisation pathways

Accurate Vertical Ionization Energy of Water and Retrieval of True Ultraviolet Photoelectron Spectra of Aqueous Solutions

Ultraviolet (UV) photoelectron spectroscopy provides a direct way of measuring valence electronic structure; however, its application to aqueous solutions has been hampered by a lack of quantitative understanding of how inelastic scattering of low-energy (<5 eV) electrons in liquid water distorts the measured electron kinetic energy distributions. Here, we present an efficient and widely applicable method for retrieving true UV photoelectron spectra of aqueous solutions. Our method combines Monte Carlo simulations of electron scattering and spectral inversion, with molecular dynamics simulations of depth profiles of organic solutes in aqueous solution. Its application is demonstrated for both liquid water, and aqueous solutions of phenol and phenolate, which are ubiquitous biologically relevant structural motifs

Liquid-microjet photoelectron spectroscopy of the green fluorescent protein chromophore

Green fluorescent protein (GFP), the most widely used fluorescent protein for in vivo monitoring of biological processes, is known to undergo photooxidation reactions. However, the most fundamental property underpinning photooxidation, the electron detachment energy, has only been measured for the deprotonated GFP chromophore in the gas phase. Here, we use multiphoton ultraviolet photoelectron spectroscopy in a liquid-microjet and high-level quantum chemistry calculations to determine the electron detachment energy of the GFP chromophore in aqueous solution. The aqueous environment is found to raise the detachment energy by around 4 eV compared to the gas phase, similar to calculations of the chromophore in its native protein environment. In most cases, electron detachment is found to occur resonantly through electronically excited states of the chromophore, highlighting their importance in photo-induced electron transfer processes in the condensed phase. Our results suggest that the photooxidation properties of the GFP chromophore in an aqueous environment will be similar to those in the protein