l-Arabinose Conformers Adsorption on Ruthenium Surfaces: A DFT Study

Adsorption of 5 L-arabinose tautomers – one acyclic and four cyclic (α and β, pyranose and furanose) species – on a ruthenium surface was studied as a precursor-process of the, nowadays more and more, industrially important sugar catalytic hydrogenation on metal surfaces in water medium. The study was mostly referred to a 37-atom metal catalyst fragment, even though border-effects on the adsorption processes were also checked employing a 61-atom metal fragment. In order to figure out conformational effects on the title process the tautomer flexibility was, at first, investigated by the genetic-algorithm based code Balloon, considering the conformational spaces of the different aquo tautomers. On the whole, 30 L-arabinose conformers, representing the complete conformational set (of a “realistic” water solution), were isolated by the genetic-algorithm based code Balloon. These were further refined at DFT level and then analyzed when interacting with a ruthenium surface, always at DFT level, by SIESTA. It was found that i) cyclic L-arabinose tautomers give rise to less strong adsorption than the acyclic tautomeric form; ii) L-arabinose molecules preferentially adsorb perpendicularly to the metallic surface; iii) one among the α-pyranose and one among the β-furanose derivatives are largely the most abundant adsorbed species; iv) the dominant L-arabinopyranose and L-arabinofuranose surface configurations are clearly related to corresponding not-adsorbed species that preserve both conformations and intramolecular hydrogen bonds during their the adsorption. The consideration of the points above allowed us to pick out significant properties, characterizing L-arabinose adsorption on ruthenium.