Enhancing Enantiomeric Separation with Strain: The Case of Serine on Cu(531)

Serine has two enantiomers, d and l, which exhibit identical physical and chemical properties but have dramatically different physiological effects. For the pharmaceutical industry, it is very important to be able to separate both enantiomers. Here we study the enantioselectivity of the (531) surfaces of Cu, Ag, Au, and Pd using density functional theory with an accurate treatment of the van der Waals interactions. Among these surfaces, it is found that Cu(531) is the most efficient for energetically separating serine enantiomers. This greater efficiency is ultimately related to a conformational strain imposed in serine and most of all in the supporting substrate. Motivated by this, we decorated the step sites of Cu(531) with Ni atoms and showed that serine enantioselectivity increases by 36% as compared to that of pristine Cu(531). These results suggest that efficient enantiomeric separation of small chiral molecules could be achieved with bimetallic stepped surfaces for which strain, both in the surface and the molecule, increases significantly upon deposition.