Surface Reactivity at “Chiral” Platinum Surfaces

Abstract

The electro-oxidation of d- and l-glucose has been investigated using the chiral electrode Pt{643}R and its enantiomorph Pt{643}S. Both electrodes are demonstrated to be enantioselective. We ascribe this behavior to the inherent (left or right) “handedness” of kink sites present at the surface. In contrast, no difference in d- and l-glucose oxidation could be detected using stepped Pt{211} and Pt{332} electrodes. Stepped surfaces are achiral, since they lack the prerequisite necessary for the observation of chirality, namely kink sites. For Pt{531}, a surface which contains only kink sites, a diastereomeric product excess of ∼80% is estimated for d- and l-glucose oxidation. This compares with a value of ∼60% for Pt{643}. Hence, the chiral discrimination appears to scale with the surface density of kink sites. These findings constitute the first experimental proof that chiral discrimination is an intrinsic property of kinked single-crystal surfaces.