Adsorption of (S)-glutamic acid induces segregation of Ni at bimetallic Au/Ni surfaces

The adsorption of the catalytically important chiral modifier, (S)-glutamic acid, was investigated on bimetallic Ni/Au surfaces created by annealing thin Ni films on Au{111}. Reflection absorption infrared spectroscopy revealed that adsorption of (S)-glutamic acid at room temperature resulted in the immediate formation of pyroglutamate species on Ni-rich surfaces and the non-zwitterionic glutamic acid species on Au-rich bimetallic surfaces. For Au-rich bimetallic surfaces, TPD revealed that pyroglutamate is also formed on annealing. Medium energy ion-scattering studies showed that significant adsorbate-induced Ni segregation was observed on Au-rich bimetallic surfaces – the driving force for segregation is likely to be the formation of nickel pyroglutamate. The implications of our findings for enantioselective catalysis are discussed.