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Guanine Assemblies on the Au(111) Surface: A Theoretical Study

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It was found previously [Small2009, 5, 1952 and Angew. Chem., Int. Ed.2005, 44, 2270] that guanine molecules when assembled in a vacuum on the Au(111) surface at room temperature form a hydrogen-bonded network consisting of guanine quartets of the same chirality; this was supported by ground-state density functional theory (DFT) gas-phase calculations. In this Article, we re-examine this system and show that many more (almost equally stable) both homo- and heterochiral structures are possible; however, the homochiral structure observed experimentally becomes definitely the most favorable only if the vibrational contribution to the free energy is accounted for. Interaction with the gold surface, considered within a continuum model, is found to be of minor importance for the comparison of different structures stabilities. We also discuss in some detail the phase transition to another heterochiral guanine phase found upon annealing as reported previously [Small2009, 5, 1952]. We find that, within the current...