Tyrosine derivatives assembled on gold.

Two different tyrosine derivatives, one with the OH group free and one with the OH group phosphorylated, linked to 3-mercaptopropionic acid through an amide bond are adsorbed to gold surfaces. The adsorbates are studied by means of X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IRAS). The techniques are used to investigate the coordination to the surface and the molecular orientation of adsorbates relative to the surface. Molecular surface interactions, causing chemical shifts in the core level XPS spectra of the adsorbates on gold, are investigated using multilayer films as references. Angle-dependent XPS, XPS(theta), and IRAS are used to estimate molecular orientation relative to the surface. The tyrosine derivatives adsorb chemically to the surface through the sulfur atoms and highly organized monolayers are formed with the OH and the PO(2-)(3) exposed to the air/vacuum interface.