Methylation of DNA nucleobases is an important control mechanism in biology applied, for example, in the regulation of gene expression. The effect of methylation on the intermolecular interactions between guanine molecules is studied through an interplay between scanning tunneling microscopy (STM) and density functional theory with empirical dispersion correction (DFT-D). The present STM and DFT-D results show that methylation of guanine can have subtle effects on the hydrogen-bond strength with a strong dependence on the position of methylation. It is demonstrated that the methylation of DNA nucleobases is a precise means to tune intermolecular interactions and consequently enables very specific recognition of DNA methylation by enzymes. This scheme is used to generate four different types of artificial 2D nanostructures from methylated guanine. For instance, a 2D guanine windmill motif that is stabilized by cooperative hydrogen bonding is revealed. It forms by self-assembly on a graphite surface under ambient conditions at the liquid-solid interface when the hydrogen-bonding donor at the N1 site of guanine is blocked by a methyl group.

By means of density functional theory calculations, the reaction mechanisms of H 2 O 2 synthesis on three low index and two stepped Au surfaces have been investigated in detail. This study shows the activation energies of five elementary reaction steps of H 2 O 2 synthesis, which include two hydrogenation and three decomposition steps of key species, are a function of reaction energies, which observe the Brønsted-EvansPolanyi rules on both the flat Au surfaces and the step edge sites of stepped Au surfaces. This study not only provides a simple method to estimate the reaction barriers of elementary steps of H 2 O 2 synthesis by the reaction energies but also predicts the catalytic performances of Au nanoparticles applied in real catalysis.