Observation of Uniaxial Negative Thermal Expansion in an Organic Crystal We thank the staff of the Swiss–Norwegian Beam Line for their kind assistance and the Swiss National Science Foundation for financial support. H.B. thanks the Danish Research Agency for further financial support.

A helix that expands on cooling: The crystal structure of TrpGly⋅H2O consists of helical peptide nanotubes extending throughout the crystal. The thermal expansion is negative in the helical direction (see graph; a axis: red, c axis: blue). This effect is believed to be linked to the increasing order of water molecules enclosed in the helices.