University of Cambridge Research Highlights Surface Science Group Home Department of Chemistry University of Cambridge

More about amino acids on Cu{311}

Following up our earlier work about the forms of chirality seen in amino acid overlayers on Cu surfaces, we have been looking in more depth at alanine - both enantiopure and racemic - and glycine on Cu{311}.

In our latest work, we have mapped out the conditions under which various L-alaninate structural phases are formed, using LEED and STM . We have also established the bonding configurations associated with these phases, using RAIRS measurements and DFT-based calculations of normal mode frequencies.

The most stable overlayer has the (2,1;1,2) structure that we reported before. Alaninate is bonded through the amine N and both carboxylate O atoms ('mu-3' bonding), accounting for all surface-layer Cu atoms at 0.33 ML coverage. At higher coverages, we now know that two ordered structures form, usually coexisting. These have (6,4;1,2) and (7,4;1,2) periodicities for L-alaninate; a fraction of the alaninate moieties are bonded through the amine N and just one of the carboxylate O atoms ('mu-2' bonding).

L-alaninate overlayers on Cu{311}. (2,1;1;2) structure, showing occasional translational domain boundaries (LH panel); coexisting (7,4;1,2) and (6,4;1,2) structures, (RH panel, upper left and lower right, respectively). (Images 10 nm x 10 nm, 78 K.)

The (2,1;1,2) structure has a symmetric lattice, while the crystallography of the {311} surface orientation obviates the 'footprint chirality' seen for mu-3-bonded amino acids on Cu{110} and {100} surfaces. The higher-coverage structures, meanwhile, both have chiral lattices (i.e. breaking the clean-surface mirror symmetry), implying that chiral nearest-neighbour interactions lead to long-range chirality in the self-organisation.

The (2,1;1,2) structure at 0.33 ML is also seen when we move from enantiopure alanine to racemic alanine or to glycine. At higher coverages, periodic chiral-lattice structures are not seen, but chiral translational domain boundaries are seen in both cases. Racemic alaninate overlayers exhibit regions of L-like domains and regions of xD-like domains, alternating over a 10 nm length scale. The chiral boundaries seen with glycinate are even shorter (1-2 nm) and arranged less regularly, but occur despite the fact that glycine does not have a chiral centre. The primary effect of the presence/absence and position of the methyl group, therefore, is on the lengths of the boundaries.

L-alaninate (LH), racemic alaninate (centre), glycinate (RH) overlayers on Cu{311}. (Each 20 nm x 20 nm, 78 K.)

Related publications

"Self-organized overlayers formed by alanine on Cu{311} surfaces"
D.C. Madden, I. Temprano, M. Sacchi, M. Blanco-Rey, S.J. Jenkins and S.M. Driver
J. Phys. Chem. C 118 (2014) 18589

"On the role of molecular chirality in amino acid self-organisation on Cu{311}"
D.C. Madden, M.L. Bentley, S.J. Jenkins and S.M. Driver
Surf. Sci. (2014) available online

[Viewable With Any Browser] [Valid HTML 4.01 Transitional]

Last updated 4/9/2014 by smd37 -at-