CHIRAL-SYMMETRY BREAKING DURING THE SELF-ASSEMBLY OF MONOLAYERS FROM ACHIRAL PURINE MOLECULES

Scanning tunneling microscopy was used to investigate the structure of the two-dimensional adsorbate formed by molecular self-assembly of th e purine base, adenine, on the surfaces of the naturally occurring min eral molybdenite and the synthetic crystal highly oriented pyrolytic g raphite. Although formed from adenine, which is achiral, the observed adsorbate surface structures were enantiomorphic on molybdenite. This phenomenon suggests a mechanism for the introduction of a localized ch iral symmetry break by the spontaneous crystallization of these prebio tically available molecules on inorganic surfaces and may have some ro le in the origin of biomolecular optical asymmetry. The possibility th at purine-pyrimidine arrays assembled on naturally occurring mineral s urfaces might act as possible templates for biomolecular assembly is d iscussed.