Thin layers of water on biomolecular and other nanostructured surfaces can be
supercooled to temperatures not accessible with bulk water. Chen et al. [PNAS
103, 9012 (2006)] suggested that anomalies near 220 K observed by quasi-elastic
neutron scattering can be explained by a hidden critical point of bulk water.
Based on more sensitive measurements of water on perdeuterated phycocyanin,
using the new neutron backscattering spectrometer SPHERES, and an improved data
analysis, we present results that show no sign of such a fragile-to-strong
transition. The inflection of the elastic intensity at 220 K has a dynamic
origin that is compatible with a calorimetric glass transition at 170 K. The
temperature dependence of the relaxation times is highly sensitive to data
evaluation; it can be brought into perfect agreement with the results of other
techniques, without any anomaly.Comment: 4 pages, 3 figures. Phys. Rev. Lett. (in press