In biomineralization, inorganic materials are formed with remarkable control of the shape and morphology. Chirality, as present in the biomolecular world, is therefore also common for biominerals. Biomacromolecules, like proteins and polysaccharides, are in direct contact with the mineral phase and act as modifiers during nucleation and crystal growth. Owing to their homochirality--they exist only as one of two possible mirror-symmetric isomers--their handedness is often transferred into the macroscopic shape of the biomineral crystals, but the way in which handedness is transmitted into achiral materials is not yet understood at the atomic level. By using the submolecular resolution capability of scanning tunnelling microscopy, supported by photoelectron diffraction and density functional theory, we show how the chiral 'buckybowl' hemibuckminsterfullerene arranges copper surface atoms in its vicinity into a chiral morphology. We anticipate that such new insight will find its way into materials synthesis techniques.
The self-assembly of the C38H14-buckybowl, a fragment bowl of the C70 fullerene, has been studied with scanning tunneling microscopy on the Cu(111) surface. Isolated molecules adsorb bowl opening-up with the center C6 ring parallel to the surface. In extended 2D islands, however, 1/3 of the molecules are oriented such that the bowl opening points down. From a detailed analysis of relative orientation of the molecules, the nature of intermolecular lateral interactions is identified. In densely packed islands, π-π bonding between convex sides of the bowls dominate, while π-H bonding between rim and convex sides plays the important role in small molecular 2D clusters.
In a recent letter on the "Optical activity from racemates", discussed at the 16th International Conference on Chiroptical Spectroscopy in Rennes (June 2017), scientists claimed to have measured the circular dichroism of colored, racemic crystals of two transition metal complexes, observations that "serve to correct a clear deficit in our understanding of the optical properties of racemates." In fact, there is no deficit in our understanding of the optical properties of racemates. Moreover, the measurements presented are unconvincing as evidence of circular dichroism measured in anisotropic crystals and therefore do not inform our understanding of the specific crystals investigated, or racemates generally speaking.
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