Rasmita Raval1

1, University of Liverpool, Liverpool, , United Kingdom

Chiral surfaces can be created by the adsorption of intrinsically chiral molecules, with the handedness defined by the molecule [1-4]. Additionally, a second manifestation of chirality may arise due to the molecule-substrate interaction in the form of a chiral adsorption footprint. Thus, chiral surfaces may possess both handedness and ‘footedness’ [5-8]. How both these aspects unfold and express themselves in organized molecular layers is little understood. This talk will illustrate how the ordering of handedness and footedness within organised assemblies of amino-acids on a Cu(110) surface can be tracked at the single-molecule level. The complex behaviour observed can be understood on the basis of three simple generic rules [9]. Using these rules, it is possible to generate every possible footprint and enantiomer arrangement that could be expressed by an amino-acid monolayer. A truly surprising level of complexity in chiral ordering behavior emerges, with a manifold of possible outputs, ranging from segregations of chirality into separate enantiopure assemblies, to ordered racemic compounds with heterochiral unit cells, to solid solutions where chirality is randomly distributed. This complexity in output can emerge at either the handed or the footed levels, leading to highly complex combinations and permutations.

[1] M.Ortega-Lorenzo, C.J.Baddeley, C.Muryn and R.Raval, ‘Extended Surface Chirality from Supramolecular Assemblies of Adsorbed Chiral Molecules’, Nature, 404 (2000) 376.
[2] R.Raval, 'Molecular Assembly at Surfaces: Progress and Challenges', Faraday Discussions, 204 (2017) 9-33
[3] P. Donovan, A. Robin, M. S. Dyer, M. Persson, R. Raval, ‘Unexpected Deformations Induced by Surface Interaction and Chiral Self-Assembly of Co(II)-Tetraphenylporphyrin adsorbed on Cu(110): A combined STM and Periodic DFT study’. Chemistry, A European Journal, 16 (2010) 11641.
[4] S.Haq, N. Liu, V.Humblot. A.P.J.Jansen, R.Raval, ‘Drastic Symmetry Breaking in Supramolecular Organization of Enantiomerically Unbalanced Monolayers at Surfaces’. Nature Chemistry, 1 (2009) 409-414.
[5] M. Forster, M. Dyer, M. Persson and R.Raval, ‘Probing Conformers and Adsorption Footprints at the Single-Molecule Level in a Highly Organized Amino Acid Assembly of (S)-Proline on Cu(110)’. J. Am. Chem. Soc., 131 (2009) 10173-10181.
[6] M. Forster, M. Dyer, M. Persson and R.Raval, ‘2-D Random Organization of Racemic Amino-Acid Monolayers Driven by Nanoscale Adsorption Footprints: Proline on Cu(110)’, Angewandte Chemie Int. Ed., 2010 (49), 2344-47.
[7] A.G. Mark, M. Forster, R. Raval, Recognition and Ordering at Surfaces: The Importance of Handedness and Footedness. ChemPhysChem 12 (2011)1474.
[8] M.Forster, M.S. Dyer, M. Persson, R.Raval, Tailoring Homochirality at Surfaces: Going Beyond Molecular Handedness. J. Am. Chem. Soc. 133 (2011) 15992.
[9] M. Forster and R. Raval, Simple rules and the emergence of complexity in surface chirality
Chemical Communications, 52 (2016) 14075.