"pop-On and Pop-Off" Surface Chemistry of Alanine on Ni{111} under Elevated Hydrogen Pressures

The coadsorption of hydrogen with a simple chiral modifier, alanine, on Ni{111} was studied using density functional theory in combination with ambient-pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy at temperatures of 300 K and above, which are representative of chiral hydrogenation reactions. Depending on the hydrogen pressure, the surface enables protons to "pop-on and -off" the modifier molecules, thus significantly altering the adsorption geometry and chemical nature of alanine from anionic tridentate in ultrahigh vacuum to predominantly zwitterionic bidentate at hydrogen pressures above 0.1 Torr. This hydrogen-stabilized modifier geometry allows alternative mechanisms for proton transfer and the creation of enatioselective reaction environments. © 2018 American Chemical Society.Engineering and Physical Sciences Research Council M.S.I. Foundation Royal SocietyThe research leading to these results has received funding from the UK’s EPSRC through grants EP/G068593/1 and EP/ H015493/1. M.S. acknowledges the Royal Society for funding his fellowship and the HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), for use of the ARCHER UK National Supercomputing Service. The authors also thank the staff of ALS for their help during the experiments