Role of Dynamics in Self-Organisation of Amino Acids on Coinage Metal Surfaces

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Biomolecules exhibit a number of subtleties in their chemistry that have profound impacts upon the roles they play in living systems. Amongst the most important are their propensity to form special kinds of chemical bonds (known as "hydrogen bonds") and their tendency to exist in two complementary mirror image ("chiral") forms. Chirality is crucial in many biological situations because left- and right-handed forms of a molecule may behave very differently when interacting with other chiral molecules. Hydrogen bonds, on the other hand, are important because they are just strong enough to be stable at room temperature, but not so strong that they cannot be severed when necessary during biological processes. Both hydrogen bonds and the phenomenon of chirality have consequently been much studied in the context of molecular biology.Just recently, however, the behaviour of biomolecules at surfaces has received a great deal of attention, in particular focusing upon amino acids - the simple building blocks from which complex proteins are constructed according to the blueprint of DNA. Drivers for this interest include development of new biocompatible materials for medical use, biosensors (especially chirally sensitive biosensors, capable of discerning between left- and right-handed versions of otherwise identical molecules) and routes towards chiral synthesis of drug precursors (producing exclusively the left- or the right-handed version of a molecule, as required). In these efforts, the role of hydrogen bonds in dictating how molecules arrange themselves at the surface has become a key focus of attention, and appears to be strongly related to the way in which molecular chirality is manifest in the geometry of extended molecular networks. Previous studies, however, have generally been limited to reporting on the kinds of network that can be produced, but shed relatively little light on how and why they form in the way that they do. Our project aims to uncover precisely this latter type of information, through a combination of scanning probe microscopy, electron diffraction, helium atom scattering, infra-red spectroscopy and theoretical modelling. Furthermore, we aim to learn how the properties of chiral molecular networks may be tuned by interaction with hydrogen (mimicking the effects of acidity variation in solution chemistry) to alter chemical reactivity, with a view towards ultimately controlling chiral chemical reactions at surfaces.Much of our initial attention will focus upon the structures formed by amino acids on copper surfaces, where some progress has already been made by ourselves and others. Our emphasis on the dynamic and kinetic processes by which these structures are formed sets this work apart from prior studies, however, and in addition we will incorporate work on other metals such as silver and gold, which have received far less notice in the literature to date. This phase of the project will greatly advance our understanding of the link between the short-range chirality of individual molecules and the long-range chirality exhibited by the surface networks into which they self-assemble. Subsequently, we will devote considerable efforts toward understanding the role of surface hydrogen in modifying the properties of amino acids. In living cells, biological molecules exist in aqueous solution, and the pH of the water environment can have profound effects upon the reactions that may occur. At the surface, we anticipate that varying concentrations of hydrogen may mimic variations in the acidity that are so important in solution. Finally, we aim to combine our understanding of the manifestation of chirality at surfaces with our findings on the tuning of reactivity, in order to conduct chiral surface chemistry. Target reactions include transformation of non-chiral pyruvic acid into chiral alanine by reaction with (for example) urea, or into chiral lactic acid by reaction with hydrogen.