| Abstract
| - The adsorption of glycine (G) on the (0001) surfaces of α-alumina with terminations modeling increasingwater activity, O3Al (anhydrous) and (Al3O−H, O3Al−OH) (oxy-hydroxide-like) were investigated at lowcoverage. Different possible glycine conformers have been considered (neutral (NG), zwitterion (ZG), anion(AG)), as well as different binding modes and orientations toward the surface. In all cases, glycine interactspreferentially with the surface through the carboxylic group. The binding with the O3Al termination of theanhydrous oxide surface may be unidentate Al−O(C) or bridging Al−OCO−Al. The anion perpendicularunidentate form is the most stable one with an energy of adsorption of ΔEads = −214 kJ/mol. The nature ofthe Al−O(C) bond is found to be iono-covalent. On the hydroxylated surface with (Al3O−H, O3Al−OH)terminations, two types of adsorption may occur: forming only H bonds with the surface (ΔEads = −70kJ/mol) or by the combination of Al−OC and H bonds (ΔEads = −159 kJ/mol). An additional scenario wasconsidered, where glycine substitutes a surface OH group and forms an Al−O−C bond, whereas the OHgroup combines with a proton from the surface to form a water molecule that coadsorbs with gycine. Thisreaction is thermodynamically favored (ΔE = −213 kJ/mol). The ZG and AG forms are isoenergetic in aunidentate parallel mode of adsorption. It is shown that coadsorbed water has a stabilizing effect and has aninfluence on the nature of the most stable G conformer.
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