THE INTERACTION OF AMINO-ACIDS WITH METALS - METHIONINE ON GOLD

The adsorption of the amino acid methionine on thick, evaporated gold surfaces has been studied by reflection absorption infrared spectroscopy. This data shows that in the multilayer regime the methionine is adsorbed in its zwitterionic form possessing both the (COO-) and the NH3+ groups, which are involved in intermolecular H-bonding. At low coverages the methionine loses its zwitterionic form and now possesses a protonated COOH group. The molecule adopts an orientation in which the C-OH bond is directed largely perpendicular to the surface while the N-H bonds are directed mainly parallel to the surface.