Effect of Water on the Rearrangement of Hydrogen-Bonded Structures of 4-Aminobenzoic Acid on Au(111) and Ag(111) Surfaces

Abstract

Water plays a very important role in promoting the biological self-assembly process, while our understanding is limited about how water affects and reshapes the assembly structure. Herein, the water-induced assembly structures of 4-aminobenzoic acid (PABA) on Au(111) and Ag(111) are investigated by scanning tunneling microscopy and density functional theory calculations. Water molecules could break the weak-hydrogen-bonded Kagomé structure on Au(111) and the consequent four-leaf clover structure formed by intermediate hydrogen bonds between the functional groups of PABA molecules and spontaneous release of water molecules. Upon water exposure, the four-leaf clover structure remains intact on the Au(111) surface, while the water molecules can break selectively the weak hydrogen bonds connecting the four-leaf clovers on Ag(111) and form preferential hydrogen bonds with the functional groups of PABA molecules, resulting in the generation of the water-involved structure. The adsorption energy of this hydrated structure on Ag(111) is significantly lower than that on Au(111), which may be the reason that the water-involved structure only appears on Ag(111). The result provides the real-space evidence of the interaction between water and organofunctional groups related to the type of the metal surface.