Chemistry

All Wound Up

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Science  30 Jan 2004:
Vol. 303, Issue 5658, pp. 591
DOI: 10.1126/science.303.5658.591c

When achiral molecules form two-dimensional films, symmetry breaking can occur, creating chiral patterns. Huang et al. found that Langmuir-Blodgett films of an achiral molecule, an amphiphilic derivative of barbituric acid, were composed of arrays of spiral structures. Monolayers of these molecules were formed at an air-water interface and then transferred to solid supports and imaged with an atomic force microscope (AFM). The authors argue that compression of the films closely packs the aromatic rings of the head groups and that the directionality of hydrogen bonding interactions induces a preferential tilting of neighboring molecules; together, they produce spirals. The tilt appears to be a spontaneous symmetry breaking in that the circular dichroism signal is the same throughout a film, but the sign of the signal changes from batch to batch. — PDS

J. Am. Chem. Soc. 10.1021/ja036878i (2004).

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