The adsorption of adenine on mineral surfaces: Iron pyrite and silicon dioxide

The adsorption of the nucleobase adenine on surfaces of the minerals iron pyrite and silica has been studied by photoemission and soft X-ray photoabsorption spectroscopy. Pyrite samples were prepared by fracture under nitrogen followed by transfer to ultrahigh vacuum, or by cleavage in vacuum. By comparing data with multilayer spectra, adenine was found to chemisorb on pyrite, with small changes in the valence band spectrum, and stronger changes in the NEXAFS spectrum. The molecules were bonded with the molecular plane at a steep angle to the surface plane. On silica the molecule was found to adsorb at a reduced angle to the surface. The C and N 1s photoemission spectra on this surface suggest chemisorption, although the nitrogen NEXAFS spectra are similar to multilayer spectra.