H–Bonding At Metal Surfaces

A potentially general method for determining the strength of hydrogen bonds between molecules bound to metal surfaces comes from Ludwig Bartels and coworkers at the University of California, Riverside (J. Am. Chem. Soc., DOI: 10.1021/ja0724341). Hydrogen bonding, which is ubiquitous in biochemistry and nanoscience, has been studied in solution and in the gas phase. But the strength of hydrogen bonds between molecules attached to solid surfaces hasn't been measured before. Bartels' group studied interactions between anthraquinone or dithioanthracene molecules on a copper surface. The molecules align themselves into rows, with adjacent molecules connecting to each other via two hydrogen bonds involving oxygen or sulfur atoms with hydrogen atoms (anthraquinone shown). Using scanning tunneling microscopy, the group looked at the effect of temperature on the rate at which a molecule breaks off the end of a row. From the dissociation rates, the researchers determined the strengths of the hydrogen-bonding interactions, which, they found, are similar to those measured in solution and in the gas phase.