On the role of molecular chirality in amino acid self-organisation on Cu{311}

We have compared the behaviour of enantiopure alanine, racemic alanine and glycine on Cu{311} surfaces, using LEED and STM to elucidate the self-organisation. In most respects, similar behaviour is seen in all three cases. At 0.33 ML, an overlayer with (2,1;1,2) periodicity is seen: the “symmetric lattice” (SL) phase. The adsorbate, in anionic form (alaninate or glycinate), adopts a 3-point (μ3) bonding configuration. At higher coverages, networks of boundaries emerge whose orientations break the substrate mirror symmetry. The boundary structure is locally chiral. This “chiral lattice” (CL) phase involves mixed 2-point (μ2) and μ3 bonding. The CL phase reverts to the SL phase on annealing above 430-440 K. That glycinate forms chiral boundaries demonstrates that boundary chirality can occur without molecular chirality. Glycinate boundaries are very short (10-20 Å), and occur in both enantiomeric forms. Enantiopure alaninate boundaries are much longer (several hundred Å), occurring exclusively in one enantiomeric form which is tied to the molecular enantiomer used. Racemic alaninate overlayers exhibit l-alaninate-like domains alternating with d-alaninate-like domains over a length scale of the order of 100 Å. The principal influence of the methyl group, where present, is therefore on which boundary enantiomer occurs, and on the boundary lengths.