Cooperativity in the Self-Assembly of the Guanine Nucleobase into Quartet and Ribbon Structures on Surfaces.

The guanine nucleobase can self-assemble into tetrameric or ribbon structures on surfaces or in solution. The origin for the occurrence of different aggregation patterns has not yet been investigated. Herein, a quantum chemical study on the different self-assembled structures of guanine and xanthine by using dispersion-corrected DFT is presented. Theoretical investigations can be used to explain, from an electronic point of view, the differences between the experimental findings. With quantitative Kohn-Sham molecular orbital theory and the accompanying energy decomposition analysis, the hydrogen-bonding mechanism within the guanine ribbons can be disclosed and the preferred self-assembled structures under different experimental conditions can be explained. An important role of the σ-electronic system in the guanine self-assembled structures is revealed as the main factor for the switch between different arrangements on surfaces and in crystals.