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Amino acids, copper surfaces and chirality

Chirality ("handedness") is a hot topic in surface science. In a new publication, we review the current state of knowledge about chirality in amino acid overlayers on copper surfaces, and present the findings of our own recent investigation of alanine on Cu{311} and {531}.

Read the press release here.

At a surface that has mirror symmetry, overall chirality can be imposed by adding a chiral adsorbate, such as an amino acid. Our work on symmetric Cu{311} exploits the arrangement of copper atoms in this surface to remove the complication of "footprint chirality", seen in the bonding of amino acids to Cu{110} or {100}. Under the right conditions, we found that alanine on Cu{311} self-organizes into an ordered structure, in which the packing of the molecules is governed by the symmetric footprint, rather than the chirality of the molecule. Small changes to the conditions, however, give rise to a pattern of chiral boundaries, the handedness of the boundary switching with the molecular handedness. In this case, chiral interactions between adjacent molecules propagate into long-range chirality in the self-organization.


Overlayers of L-alanine (LH panel) and D-alanine (RH panel) on Cu{311}.

One can also create metal surfaces that have no mirror symmetry: Cu{531} is such an intrinsically chiral surface. In principle, left- and right-handed molecules might interact differently with, say, a left-handed surface. This is exactly what we found when we deposited L- and D-alanine on Cu{531}-S. The bonding of the molecules to the surface, combined with hydrogen bonding between neighbouring molecules, is strong enough to cause restructuring of the arrangement of copper atoms. Crucially, the chiral phases that form are different depending on whether L- or D-alanine is used: a strong enantiospecific structural effect.


Overlayers of L-alanine (LH panel), D-alanine (RH panel) on Cu{531}.

This is fundamental research, aimed at furthering our understanding of surface chirality at the level of individual atoms, molecules and bonds. Our work provides clear evidence for enantiospecific structural effects in molecule-surface interactions, effects that point towards a basis for new methods in chiral chemistry. In the longer term, we believe that these effects may be exploited practically, both for pharmaceutical synthesis using heterogeneous catalytic routes, and for enantio-sensitive bio-sensors.

We are delighted by the award of a new grant to continue this research, made by NSF and EPSRC to ourselves and to Jane Hinch (Rutgers University).


Related publications

"Chirality in amino acid overlayers on Cu surfaces"
M.L. Clegg, L. Morales de la Garza, S. Karakatsani, D.A. King and S.M. Driver
Topics in Catalysis 54 (2011) 1429
(The final publication is available at www.springerlink.com)


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Last updated 28/11/2011 by smd37 -at- cam.ac.uk