Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 56: Metal substrates: Adsorption of organic / bio molecules VI

O 56.3: Vortrag

Mittwoch, 24. März 2010, 15:30–15:45, H36

Single enantiomorphism and chiral conflict in 2D crystals — •Christian Roth, Leo Merz, Manfred Parschau, and Karl-Heinz Ernst — Nanoscale Materials Science, Empa, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland

In order to investigate chiral recognition on the molecular level, we investigated the effect of chiral doping of monolayers of tartaric acid (TA), malic acid (MA) and succinic acid (SU) with STM and LEED. We reported earlier that doping achiral SU with a small amount of chiral TA leads to single chirality (sergeants-and-soldiers effect) [1]. Here we present results of cross-contamination experiments of TA and MA. The mixture of left and right handed TA (rac-TA) shows a superposition of the two enantiomorphs in LEED that are observed for the pure enantiomers. Adding one enantiomer of MA to the mixture suppresses formation of the two enantiomorphs. (R)-MA allows thereby only the formation of the structure known for pure (R,R)-TA, while (S)-MA leads to the (S,S)-enantiomorph. Mixing chiral (R,R)-TA into rac-MA leads indeed to single enantiomorphism as well, however, this time the structure is a completely new polymorph that has not been observed for pure MA. Two different mechanisms are proposed for the observed results: an entropy driven effect in the rac-TA / MA experiment and a chiral conflict in the rac-MA / TA case.

References

[1] M. Parschau, S. Romer and K.-H. Ernst 2004 J. Am. Chem. Soc.126 15398