Formation of Hypoxanthine Tetrad by Reaction with Sodium Chloride: From Planar to Stereo.

By reacting with NaCl on Au(111), the formation of hypoxanthine (HX) tetrads is demonstrated at the atomic scale in real space. These results directly demonstrate that alternative purine tetrads can be formed in both planar and non-planar configuration, and that ionic bonding plays a crucial role for the formation and planar-to-stereo transformation of the tetrads, providing deeper insight for constructing artificial DNA/RNA quadruplexes. Moreover, both the tilted HXs and Na show strong charge transfer with the substrate in the non-planar phase. The insights gained by this work also open up new routes to tune the electrostatic nature of metal-organic interfaces and design stereo-nanostructures on surfaces.