AVS 49th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM9
Self-assembly of Chiral Nanoclusters of Cysteine on Au(110)-(1x2)

Monday, November 4, 2002, 11:00 am, Room C-108

Session: Adsorption and Chirality
Presenter: A. Kühnle, University of Aarhus, Denmark
Authors: A. Kühnle, University of Aarhus, Denmark
T.R. Linderoth, University of Aarhus, Denmark
L. Molina, University of Aarhus, Denmark
B. Hammer, University of Aarhus, Denmark
F. Besenbacher, University of Aarhus, Denmark
Correspondent: Click to Email
We have performed a comprehensive STM-based study of the adsorption of the chiral amino acid cysteine, HS-CH@sub 2@CH(NH@sub 2@)-COOH, onto the missing-row reconstructed Au(110)-(1x2) surface under UHV conditions. In experiments where we deposit cysteine either as the pure enantiomeric forms or as the racemic mixture, we have identified a rich variety of chiral adsorption phenomena. The results are interpreted with the aid of density functional theory calculations. Previously, we have reported on the enantioselective dimerization of cysteine into homochiral molecular pairs and identified the atomic-scale interactions responsible for this intermolecular chiral recognition.@footnote 1@ Here, we focus first on supramolecular chain-like assemblies of cysteine molecules that coexist with the molecular pairs. The chiral chains extend over several hundred Ångström and consist of two adjacent rows of cysteine molecules. Formation of these chains is accompanied by a pronounced surface reconstruction, involving the removal of two close-packed rows of gold atoms underneath each molecular double row, and is driven by the formation of hydrogen bonds between the carboxylic groups of the cysteine molecules in the rows. Secondly, we discuss the self-assembly of molecular nanoclusters of cysteine. When cysteine is deposited at a substrate temperature of 120 K, small, irregular agglomerates of molecules are formed. A remarkable transition is seen upon annealing to 270 K, where the molecules self-assemble into completely identical clusters with a size of 18 by 24 Å. The molecules appear to segregate into homochiral clusters when the racemic mixture is deposited. @FootnoteText@ @footnote 1@ A. Kühnle, T.R. Linderoth, B. Hammer and F. Besenbacher, Nature 415, 891 (2002).