Thermally Controlled Bonding of Adenine to Cerium Oxide: Effect of Substrate Stoichiometry, Morphology, Composition, and Molecular Deposition Technique
Abstract
The adsorption of adenine, one of the structural units of DNA and RNA, on nanostructured cerium oxide was studied using synchrotron radiation based techniques: photoelectron and X-ray absorption spectroscopies. Using a systematic approach, we studied this biomolecule's bonding to the inorganic surface and examined the effects of different stoichiometry, morphology and 'composition of cerium oxide films, as well as two methods of molecular deposition (evaporation in vacuum and deposition from aqueous solution).
The adenine molecule chemisorbs on the stoichiometric (IV) cerium oxide intact via nitrogen atoms, independent of the oxide morphology and deposition technique. Annealing of the adenine adlayer at 250 degrees C causes CeO2 surface partial reduction, along with the partial deprotonation of the nitrogen.
The reaction of adenine with ex situ prepared CeO2 films (nanostructured compact and porous) activates Ce4+ cation reduction not only on the surface but also in the subsurface layers accompanied by water desorption. The adenine molecule was found to oxidize and decompose on a reduced surface of the cerium oxide, and for a higher degree of oxide reduction, the temperature of decomposition is lower.
The concentration of oxygen vacancies on the surface determines the degree of adenine stability on cerium oxide.