Thermally controlled adenine dimer chain rotation on Cu(110): The critical role of van der Waals interactions

The theory of adenine dimer chain assembly on Cu(110) surface is controversial, due in large to the lack of an adequate description of the van der Waals (vdW) interactions. Here, we show by a combined first-principles calculation and experiment that the role of the vdW interactions is to tilt the energy balance at different levels of chain hierarchy. We find that the stable chains are made of metastable dimers, whereas the metastable chains, close in energy to the stable ones, are made of stable dimers. As such, at room temperate deposition, adenine dimers exist primarily in their stable form. This leads to the formation of metastable chains. By annealing at elevated temperature, however, more dimers can exist in the metastable form. This leads to the nucleation of the stable chains at a different orientation. The thermally controlled chain rotation is expected to be of general importance to the understanding of amino acids assembly and functionalization at the most elemental level.