Adlayer structures of -homocysteine and -homocysteine thiolactone on Au(1 1 1) surface: an in situ STM study

The adsorption of dl -homocysteine (Hcy) and l -homocysteine thiolactone (HTL) on Au(1 1 1) electrode was investigated in 0.1 M HClO 4 by cyclic voltammetry and in situ scanning tunneling microscopy (STM). Hcy and HTL molecules formed highly ordered adlayers on Au(1 1 1) surface. High-resolution STM images revealed the orientation and packing arrangement in the ordered adlayers. Hcy molecules formed ( 2 3 ×3 3 )R30° adlayer structure and H-bonds between carboxyl groups were assumed to be responsible for the origin of tail-to-tail or head-to-head molecular arrangement, while HTL molecules formed (4×6) adlayer structure, and two different orientations and appearances in the ordered adlayer were found. Structural models were proposed for the two adlayers.